As an aside - I *like* picking locks with my thief (it gives insignificant amounts of XP but I mainly do it for roleplaying). There are some (not many) locks that resisted bashing with an 18/50 strength character and potions of strength are best used for battles, knock uses up a valuable spell-slot.
Stealth is cool too though, whether you use the backstab or not you can scout enemy positions and strengths, buff-up accordingly or send an advance fireball at a group of gnolls ;)

Pick-pockets is (for me) not worth it as rarely is there something worth nicking in the game (most of the great equipment is found in dungeons/on enemies and there's plenty of money around for the stuff in shops, at least by the time you need it).

Set-traps is useful though (but perhaps more so at higher levels when you can set a few traps in ambush and do real damage).

Don't forget to scroll-down at level-up time - one or two of the thieving skills are hidden at the bottom and I missed them at first on my first playthrough.

Yes, semantics and irrelevance, since I was talking of monetary cost, and you know it. It is not a case of me taking issue at all -- who was it who disagreed in the first place, hm? Let me make this perfectly clear: any advice that I, or anybody else, gives is a purely personal preference. There is no 'right' or 'wrong' way to play a single player game, and you are not the only person to have played it "many, many times".

No, I didn't know it. Please do not assume you know what I'm thinking. Your statement made it seem to me you were more worried about the skill points and spells than anything else. As far as potions of invis, yes they cost money, but it's not like it's going to break your characters especially if you've investes a few points in Pick Pocket, which can actually net you some significant money.

You said "...do not waste points on Imoen. She is a far better scout, and all of her points should be spent on Find Traps (essential!) and Stealth." (and you've said this before in another thread as well) You, as a player that's obviously played through the game before, and addressing a player that hasn't (the OP), this statement comes across as an absolute and a new player may think this is one of those games where if you don't build a character a certain way, you won't succeed. And this is not the case. I was pointing out that you can build Imoen quite differently and still have a successful character, depending on how you want to play the game.

Nor did I say I was, but I wanted to make it clear to the OP if he was still following this thread that I wasn't taking a different position on what to do with Imoen from a stand point being contrary just for the sake of it. I wanted to be clear that I'd played the game many times just the way I suggested Imoen could be built and played and didn't have a problem with her. It's all play style.

My apologies, as, from the tone of your post, it I now do seem to have offended you.

"Please do not assume": You have not offended me in the slightest, but I am done with this silliness.

This seems to have gotten out of hand. If I might ask another: It was mentioned you can elude the guards, but will any NPCs be upset with you if you return after they called the law for you having stole from them?

If you offend an NPC by such an action they will turn hostile, but because of their status they will not attack, but run away -- this is when the guards get called. If you wait in another area for a length of time (8 hours is plenty, usually), and then return, the guards will have gone but the NPC/s will still be hostile. They will not re-call the guards for the first offence, but should you attack and kill them you will lose a lot of reputation.

So, it could theoretically be easy to break a quest just by opening someone's cabinet? I don't get it, I never saw any guards or fleeing NPCs so far when I took stuff.(Just acquired the druid and fighter)

Well yes, that's what choice is all about. This is not a linear game like IWD, and you may complete quests or not, or simply ignore them. But don't worry, you won't break essential storyline quests. When I said NPCs flee, I meant that they avoid you (they won't attack), but generally won't leave the building. You won't alert guards at every single chest you come across. The type of places to beware of are private homes, inns, shops etc. To test this out (save first) go upstairs (top floor) in the Friendly Arm Inn and you will find a nobleman in the first room on the left. Steal from his room and you will soon be accosted by guards, and your chance at receiving the Golden Pantaloons will be gone, if you haven't already got them. :)

So, it's less straightforward when it's "stealing"? I think I took something from a cabinet in the beggar's room, but that wasn't "his"?

Yes, some areas and chests are regarded as public -- barrels and chests outside for instance -- but if you go into a private room that's different.

1) Yes. If they are people nearby, especially in towns, there is a high chance for guards to be summoned. And almost all of them are not able to be bribed (which means combat, reputation fall, or if you are low level, maybe your death too). That aside, most containers, even if locked, contain trash, or even nothing at all. Sound exceptions to that are underground places, caves, dungeon-like areas etc.

2) With high strength roll (18/00) you can open many locked things (doors, chests), just by attacking them as if they were enemies. A thief can pick locks too, but needs to be high level relatively and spend points in "open locks". Finally, the best solution is the wizard spell knock. Unless something is not supposed to open (scenario/content/area wise), it never fails to do your dirty job.

3) Many npcs have quests/requests of their own. Taking your time at your leisure makes them angry, usually; especially so if they are evil. But solving the mine's problem is your biggest priority in this game; your normal weapons will keep breaking, even during combat sometimes.

4) Dualclassing with anything else besides from a fighter to something else, is most of the times considered a poor idea, and/or pointless. Except for thief/mage, cleric/mage and other combos. If you have a wizard, it is best to keep him as is; spellcasting is broken and cheesy all by itself in BG saga. And go get that ring of wizardry from the Friendly Arm Inn map, and the ring of Wizardry from Razamith in Baldur's Gate!

Best of luck and enjoy your play. You can always start a second playthough with another character, once you get to learn the game well.