The barbarian does feel a lot more powerful now at level 20, this wasn't the case in chapter 1 though :)

What were the starting stats and which stats did you raise at level ups ?

Can't speak for otjp but I'd imagine he maxed out his strength and applied every stat increase afterwards to strength. I'd guess he has a very high constitution, good dexterity and wisdom, and then dumps intelligence and charisma.

Starting stats were 20 16 18 1 18 1. First 2 stat points went to dexterity to get it to 18, then all points since have gone into strength. Current stats at level 20 are 23 18 18 1 18 1.

Why exactly did you go for 18 dexterity there? Do you really use the throwing axe enough for that to be worthwhile over more strength?

It was for the boost to reflex saving throws and AC. Don't use the throwing axe in this game, the range is too short, in IWD the throwing axe had good range but it seems to have been shortened. Rely on the sling for ranged attacks.

The type of armor you wear caps your dexterity bonus to AC. Before accounting for other effect (magical buffs/items, class features, shields, etc), this is the cap for every type of armor:

Platemail is capped at 12 dexterity, for an AC yield of 19
Breastplate is capped at 16 dexterity, for an AC yield of 18
Chainmail is capped at 14 dexterity, for an AC yield of 17
Studded Leather is capped at 20 dexterity, for an AC yield of 18
Leather is capped at 22 dexterity, for an AC yield of 18

Because IWD2 doesn't actually implement the movement speed penalty for wearing heavier armor (to my knowledge Temple of Elemental Evil is the only D&D CRPG that does) there's basically no benefit for a front-line warrior to invest in more than 13 dexterity. Thanks to Barbarian fast movement, you can kite melee enemies indefinitely so range doesn't matter too much. I find the returning weapons a lot more convenient than slings, which eat through expensive ammunition whenever you want to use them. Being able to just sell all that magical ammunition enemies drop generates a boat-load of cash.

The problem is that there are very few types of armor that cap out exactly at 18 dexterity. Most armor either has a lower or higher cap, so it's actually very unlikely you'd find a suit that gave an optimal value at 18 dexterity, and it's even less likely it'd beat out an equivalent suit of full plate.

I don't remember the exact armors clearly, so I checked a guide for the best varieties of armor. The best suit of full plate in the game comes out to +10 armor and caps at 14 dexterity, for a total of +12 to AC. The best suit of leather/studded leather comes out to +6 armor and caps out at 22 dexterity, for a total of +12 to AC. The best suit of chainmail is +7 to armor and has no dexterity cap, but only surpasses those other options at 22 dexterity when it hits +13 to AC in total.

I did a quick run through of the lesser armors, but there was nothing that stood out as outclassing non-magical fullplate (+8 armor, caps at 12 dexterity, for a total of +9 to AC, a mere 3 points away from the best armors in the game).

But after Dragons Eye, sling ammo won't be a problem. There's a chance to get a returning fire bullet +1 which all but nullifies the need to hoard bullets

I did play a half-orc barbarian with maxed str, dex,con, 16 wis, dumped int and cha and put everything at level up in strength, the faster you kill stuff the better.

Wisdom is totally overrated, there's a feat which has the same effect as +4 wis for non-priests but I didn't even bother taking it.

Iron Will works best when you're stacking it with an already decent wisdom modifier, a magic item to boost your saves, and a magic buff to boost them further. The baseline low saving throw progression gives you only +6 to your weakest saves by the 20th level, but if you keep adding bonuses getting into a nicer range like +20 is totally doable, which completely changes what you can do.

Of course, as always, you're much better off proactively eliminating spellcasting threats than trying to shrug off their spells after the fact.

Spellcasters are usually my first target in a fight.

Regarding the sling bullets, I've had no problems with running out, used the basic ones as well and the rarer ones. Gold is in abundance so stocked up when I came across any.

Mastered the eight chambers. Was straightforward to complete, didn't need to heal from start to finish, only rested once before the last chamber to get the uses of rage back, didn't even equip regeneration items when resting so only healed 1 hp point over eight hours as damage to that point was minimal, it was only in the last chamber that I took much damage but the brass monks fell fairly quickly. The exp was what made it worth doing. Went from level 20 to 22 with the exp from this monastery.

The four iron golems are down, those things hit hard, used my sling+2 with +5 bullets to take out three of them, then went in with the brilliant short sword to finish the last one off. They don't take too many hits to kill, 4 or 5 I think they took, but they seem to have a lot of resistances.