I am playing NWN1 OC right now with a rougue/fighter/blackguard and its really fun.
I have read a lot in the wikias for NWN1+2 but some questions are still open.

1) All tables regarding spell progression go from lv1 to 20.
Does this mean a caster does not learn new spells known and new spell slots above lv20?

example: First you take 5lv fighter, afterwards you take only levels as wizard.
Does this mean you will learn new spell until character lv 25 (= wizard lv 20) and then you get nothing
from more levels of wizard?
note: this is for understanding the principle, NOT if such a build makes sense

Is there a difference between NWN1 and NWN2?

2.) in NWN1 you do NOT get more attacks per round after character lv20 but in NWN2 you do, right?

3.) Right now I have not a big problem with traps (half of my levels are rouge and I max out open locks, spot and disable traps, tumble and UMD) but I want to use a char that is mostly cleric when playing sou/hotu.
The worst trap till now made 107 points of damage and I´m only in chapter2.

In sou/hotu you can have 2 henchmen. If one of them is rouge, can you tell him to spot and disarm traps?
Else I will find lots of bizarre deaths or I use a spell that protects from elemental damage in every dungeon.

4.) Now I go out and explore the world until my weight limit is reached and then I return to town with the stone.
Fortuanatly my char is strength based.
How are you supposed to play the OC of NWN1 with a mage (or another char with little strengh)?
I stopped playing "batrayal at kronor" in chapter 3 because I was tired of running back to the shop after every second fight.

In NWN2 you don´t have this problem since you are a big group and you can use everyones inventory.

5.) In NWN1, can you put executable combat actions (like knockdown) to your quick slot? In NWN2 you can pull things from your feat list to the quick slot, but in NWN1 this seems not to work. Using the ring menu in combat is not so great.

Correct on both counts, except for the 'get nothing from more levels of Wizard'. While you don't get more spell levels or spell slots for levels above 20 in the casting class, you will get better spell durations, better spell penetration, and epic bonus feats, which can be used to grab Epic Spells. Yes, NWN1 uses the 3.0 rules and NWN 2 uses the 3.5 rules. While they're very similar rule sets, there are some significant differences. As well, NWN2 made some changes in stacking rules (in NWN1 you could stack ability score boosts from various sources, for example, while in NWN2, only the highest bonus applies). NWN1 only allows a maximum of 3 classes when multiclassing, while NWN2 allows 4. There are some other differences as well (some races and classes available in NWN2 that aren't available in the first), but those are some examples that spring to mind right away, No. You don't get more attacks per round in either game after level 20, if memory serves. I could be misremembering on that though, as it's been quite some time since I've played NWN2. Yes, you can have them go into Search mode. Use magic bags and boost your Strength with spells/items/potions. You'll still have to run back and forth eventually, but you can always make it a habit to only keep items that are of good value for their weight (it doesn't take long to figure out which ones are worth it). In NWN1 just right-click on your quickslot, then navigate the radial menu to select the action you want in the slot and select that action. This will load it into the slot for quick use.

When it comes to carrying gear, in SoU and HotU, you can access your henchman's inventory, which means a strong henchman can carry gear for you. (I use the TonyK AI modifications for henchmen for the OC and expansions; that allows me to access henchman inventory in the OC as well.)

Though as previously mentioned, magic bags are the most powerful magic items in the game.

When it comes to traps and locks, the entirely indispensable skill is Search. Disarm is extremely helpful; but the cleric spell Find Traps can disarm them, available not only as a spell but on scrolls and certain items (when you find them). Any weapon that does elemental damage will bash just about any chest or door in the game. For trapped doors or chests, missile weapons that do elemental damage will bash them from a safe distance. At lower levels, it's hard to get by without the rogue's open locks and disarm traps; at higher levels you have options, but I don't know of a good replacement for the Search skill. (I am taking about NWN1 here; I haven't played through NWN2,)

Completely forgot about Find Traps; the name doesn't quite give away that it's both search and destroy. NWN2 is much more party oriented, so you can always have someone in the party to deal with these situations. For most of the OC you'll be packing 3-4 companions, more than enough space for a rogue.

Thankns, now I have a new question about this.
What about prestige classes where you continue to get spells in your old class?
Like you take 10lv wizard, then 10lv pale master, then another 10lv of wizard.
In this case you will learn new spells until character level 25, because you get
new spells at every odd PM level, if I get your post right. OK, for hou/hotu I will make a cleric (domains air and magic to get some offensive and defensive power like a mage) and take 4 levels paladin until lv20. I don´t care if I get lv9 spells early since this will be more like a self buffed fighter who can summon some friends.
I don´t want to take levels of fighter again because I had this in everything regarding NWN till now.
This is my first step towards a caster main char. Maybe i try an arcane caster somewhen in the future.

I have a great idea.
(this is the moment where you should scream "Don´t do it" and start running :)

Can you put full magig bags into emty magic bags to ruduce wight even further?

Yes, that's correct. The game looks at effective caster levels, not actual class level. So a Wiz 10/PM 6 is effective caster level of 13. That will net you a BAB of +16 by level 20 for a full attack routine. However, I'd suggest actually taking Fighter so you can grab Weapon Specialization (and later on take a couple CoT levels or more FTR once your character is in epic levels, so you can grab Epic Weapon Specialization). But there's nothing wrong with the Pally levels either though.

On a side note, a Cleric is probably the only class where having less than +15 BAB isn't a bad thing, since you can buff yourself with Divine Power to get a BAB of a FTR of equal level. It used to be that any extra attacks granted by this spell were at your highest BAB, but something tells me this was changed in the final patch. If not, this is a huge advantage. If it was changed, then it's still a nice spell, but not nearly as great. A great idea, but unfortunately it won't work. The game will just tell you that you can't put one bag into another (it will give you a message along the lines of 'invalid container' or something similar like when you try to put a potion in a gem bag in Icewind Dale).

This is correct; you will continue to learn spells until you have the effective spellcasting of a 20th level wizard. Caster level also continues to accrue normally.

It's worth noting that Pale Master is a horrible prestige class. You need to make careful consideration before trading away even a single caster level. A prestige class that gives away five just isn't even in the ballpark of being reasonable. Paladin will work nicely to split with cleric. You will need to play human or half-elf in NWN to get the necessary favored class on that combo, but it's pretty solid.

Please note that you won't be a primary caster with this kind of split; your spellcasting will be more comparable to that of a bard until you're well into the epic levels. So make sure you have some strong combat abilities to back it up. Not allowed, but in any case you should be able to upgrade to bags of holding (-100% weight) before this becomes a serious issue.

As a combat-oriented cleric, you should have a fairly high strength score (use magic items to boost it if you must) so this shouldn't be a huge issue. It's also worth noting that in HotU you will eventually find a merchant-in-a-bottle. Seriously, it's an item that 3 times per day will summon a merchant.

The difference between choosing 4 Fighter levels and 4 Paladin levels is whether you like the fighter abilities or paladin abilities. 4 Fighter levels get you weapon specialization and a couple of extra feats. 4 Paladin levels get you saving throw bonuses, immunity to fear and disease, and smite evil. (ETA: 4 levels of Paladin will also give you +2 to your effective Cleric level for purposes of Turn Undead.)

You could also take 4 levels of Champion of Torm instead of either Fighter or Paladin. You won't be able to choose your first CoT level until after you have at least 9 Cleric levels, have a Weapon Focus and you are not evil. You will get the CoT save bonuses, smite evil, and a couple of extra feats. A disadvantage of this route is that you have to either choose a weapon focus from your cleric weapons, or spend a feat on extra weapon proficiencies. (Though if you wanted to focus in something like a bastard sword, or other exotic weapons, you have to spend an extra feat on the proficiency no matter which class you mix in with Cleric.)

Just noticed this.

Air Domain is a decent domain, but I'd warn against the Magic Domain. Its "special" bonus is that it gives you access to extra spells, but the spells it gives you aren't even that great. The only good one is "stoneskin", but there are other domains ("earth", "strength", and "good" come to mind) that offer this spell along with better ones.

If you want wizard spells, the trickery or travel domain would be better choices. Trickery gives you access to the awesome invisibility spell line, and travel gives you access to considerably better spells. Haste, in particular, is an awesome spell to have.

A great spell, to be sure, but somewhat redundant in HotU, since you can get a perma-Haste item. Stoneskin as well is of limited utility since it's a high magic campaign, so any weapon of +5 or better will bypass the Stoneskin. I'd grab trickery for Improved Invisibility.

Still oodles better than the magic domain in any event.

As I have written before, I don´t want to use fighter levels because I did this in everything regarding NWN till now.
Paladin fits good to cleric (ok, fighter and some others too) and immunity to fear and disease sounds good.
These mummies in the OC are really nasty. And I want to use martial weapons early on.

About domains:
If I get the manual right, the persistend spell feat does NOT exist in NWN1. And when you get and item that gives
haste the travel domain is useless.

about trickery: I am a pally/cleric who confronts evil face to face, not a rogue. And when 2 henchman follow me and attac everything in sight invisibility becomes even more useless.

maybe strengh domain is better than magic

Correct.

You can always tell your henchmen to stand their ground if you're in a spot where you want to go invis and explore a bit ahead.

That aside though, Improved Invisibility gives you concealment, meaning a 50% chance that any attack against you will miss. That alone is reason enough to take Trickery.

But it's your character, so by all means build it the way you want. We're just tossing in our two cents.

On a side note, I quite like the Strength domain, as it gives you Divine Power as a level 3 spell as well. If you take the Extend Spell feat, this allows you to have Divine Power in levels 3, 4, and 5 slots. Which means you can pretty much have the same BAB as a Fighter of your level at all times. I used to take the Strength domain as one of my Cleric character domains a lot.