I have played most IE games but that was years ago and I also used to be a bit of a munchkin back then. Now I'm thinking about replaying IWD 1, but this time I would like to roll with the punches as much as possible and need some info about what's possible and what isn't.

My plan is to go with a party of 4, only one roll per character, no save scumming or similar. I would also love to play basically hardcore, i.e. a dead character is replaced by a new recruit.
Is that feasible for someone who is pretty decent at this type of game but has forgotten most about both the content of IWD and the D&D ruleset? Is it even possible? I seem to recall that you can add new party members at any point but do they level quickly enough or would they stay useless if they only join halfway through the campaign? Is retreat usually an option or does encounter design prevent it? Is the whole idea a recipe for frustration?

I'd say for the first part of the game replacing fallen party members with 'recruits' would work out okay, but there will come a point where the new ones, even with the larger XP awards from quests, won't catch up fast enough to be useful. I think Petrus' suggestion of having them ressed/raised would actually fit in better for your concept. After all, it's something provided right there in the gameworld itself and it will cost you both time getting to a temple (until you're able to perform the spells yourself), and resources (the cost of the spells), which gives it that much more of an impact.

You can use a stealthed or invisible character to scout ahead (and this is highly recommend if playing Iron Man), and then get an idea of what you are up against and if you need to buff or not. Ambushes are rare, but sometimes monsters seem to be able to smell or hear your invisible scout, making buffing harder.
Some fights, inside rooms, can be avoided, but most can't.

Grinding is possible in some areas; Shadows in the Vale of Shadows respawn, for example.

Alright, that sounds pretty good. I think I'll give it a shot with true permadeath and if it turns out to be too hard or simply not fun due to obviously not being considered in the original design I'll switch to resurrection. I could then still make this more painful by raising the price or whatever.

It's also probably a good idea to start with a party of 6 to lessen the blow if anyone bites it. Anything else you think I absolutely have to consider before trying this? Do I need a particularly good roll to be able to successfully stealth?

High skill and being in shadows both when first trying to hide and when rechecking the skill (every 6 or 10 seconds) are the keys. It takes some practice, but you'll get the hang of it. In the beginning the skill checks will fail a lot, though.
I'd recommend a Halfling Fighter/Thief for the job. IIRC Halflings have the highest sneaking skills, and a F/T will be excellent for backstabbing.

Also, if you want an easier game you could include a Bard in the party. The War Chant of the Sith which they get at lvl 6 or therabouts regenerate hit points making healing spells and potions mostly redundant.

Stealth is checked every round, so there's always a chance for failure. In this regard, invisibility is a much better option if you have it available. Still, stealth can be very useful, so make sure your thief has his stealth skills maxed if you're planning on going that route.

As to running from battles, you can certainly do this in many places, but be aware that the mobs will follow you except through transitions. So whatever you're engaged with will have to be fought anyway. Running can give you a few moments to buff and/or heal though. I'd recommend considering using your Cleric as a heal-bot for this type of Iron Man run. Get him in Sanctuary and then constantly cast healing spells on the tanks while in battles. Rest restrictions will obviously mean you're going to have periods where you've run out of spells though.

As far as raise/res, the scrolls sell for around 350 gold for Raise and 10000 gold for Res. To get the service done in the temple is around 3500 gold for Raise and 7500 for Res (the pricing here is odd, IMO - one tenth the price for a scroll of Raise while the scroll of Res is more than the price of the service? Odd) Do keep in mind that prices fluctuate depending on your CHA, so you may get somewhat different pricing.

Great, it sounds as if it's at least worth a try to go ironman and I can always soften the rules if it doesn't work.

I'd prefer to mark both of your answers as the solution but since that's impossible I'll go with the first one and +1 the rest. Thank you guys both, you help is very much appreciated!

Hopefully I can get this thing started over the weekend, really looking forward to it.

Keep us updated. I'm interested to hear how it goes. :)

Alright, I rolled a party -no reroll no reallocation of points- and played the prologue but found that the combination of 6 guys with very weak stats and permadeath makes it impossible not to cheese like crazy. Since I'd like to keep the permadeath I've decided to start over and at least allow myself to roll a decent party to get some margin for error.

Reallocation of points makes dual classing possible but the manual is very vague about it unfortunately. I'm familiar with the stat requirements, but have 2 questions regarding weapon proficiencies:
1. If I dual from Ranger to Cleric, can the character use all weapon types once the Ranger levels become active again or is the dual character restricted to Cleric weapons? Same question for Fighter dual to Druid.
2. Are weapon proficiencies cumulative over both classes, i.e. can I spend 2 points on Mace while the character is a Ranger, spend another while he's a Cleric and have 3 as soon as he's both or does he only get the highest proficiency of any one class?

Edit:
Just thought of a 3. question that's not handled in the manual afaik: What's the upside of using 2-handed weapons? Was it something like bonus damage from strength...?

1. Clerics can only ever use cleric restriced weapons, no matter what skills and other class they have.
2. I think they are cumulative, but I wouldn't swear on it.

Ah, that's what I thought. Thanks!

Would be very nice, but it looks implausible to me given that neither the Ranger nor the Cleric could ever get more than 2 points on their own. The problem is that you can't really try it out without risking to lose the prof. point. Hopefully someone knows for sure.

No, they are not cumulative. Don't waste points in your second class that you already have in your primary class. In your scenario, when you get your primary class back you will still only have 2 points (the highest) in Mace. Damage dealing (D12) and reach: 2-handed weapons can be used behind a tank with sword/shield, for example, just like staves.

It's hard to use 2H weapons as elongated weapons in the game due to no grid. The upside of them is that they generall deal more damage.