Remember the golden rule with 3rd edition: keep your attribute scores even rather than odd. I'd say this is one area where you can go multi-class without breaking your theme. Fighter/Barbarian is a great combo that stays true to its "pure warrior" roots while giving him a nice balance of muscle and feats. My suggestion would be a half-orc with 20 strength. You might consider Druid, but otherwise Cleric is your go-to choice. Remember that unlike the 2nd edition games there aren't any hard rules on what weapons a Cleric can use; if you multi-class (even one level) as a fighter or invest a feat in weapon proficiency, you can use whatever you like. For some silly reason, IWD2 implemented a weaker version of the 3rd edition sneak attack rules. This makes single-class Rogues very underwhelming in combat. I was really disappointed with my party rogue in IWD2. With multi-classing veto'd, I'd say go with the bard for your thiefy character; there's not a lot to get out of sneak attacking here but the party support of the bard could be quite useful. The scroll issue isn't as bad in IWD2 as it was in IWD1; I always at least had something, even if the selection wasn't as good as I'd like. Both Sorcerers and Wizards are great character classes, and which one you choose is really up to your preference.

As for attributes, here's how it breaks down:

Strength: primary fighters should max it, those who are secondarily melee (such as clerics or rogues) should get it as high as they can afford, and everyone else should drop it to around 8-10 (which gives you sufficient carrying capacity)
Dexterity: max this out for ranged attackers. Note that this includes wizards and sorcerers! Many of their spells technically count as ranged attacks and you need to successfully "hit" the opponent for them to work. Dexterity improves your armor class, but is "capped" by heavy armor. For instance, if you're wearing platemail you get no bonus for a dexterity score above 12. You might go for 13 to meet the prerequisite for the "dodge" feat, but that's about it. For those wearing light or no armor, a high dexterity score is necessary to get a good AC.
Constitution: everyone needs this. Having at least a 14 is advisable; don't go below 12.
Intelligence: this gives you additional skill points. Many characters in your party (looking at you, fighter) don't really need that many skill points, so this makes an easy dump stat. No matter how low your intelligence score goes, you can never earn fewer than 1 skill point per level (2 if you're human!) meaning that there's a certain point at which further intelligence reductions have no further penalty and you should just drop it down to 3. For fighters and Paladins, there's no difference between an intelligence score of 9 or 3, so either boost it higher for additional skill points or dump it. (this is why 3E normally sets "8" as a minimum ability score for point buy; IWD2 ignores this convention). Wizards should max this.
Wisdom: this affects your will saving throw. Many of the most dangerous and debilitating spells target the will saving throw, so avoid having a penalty here. For most characters, 10-12 is a good number. Paladins and Rangers should have 14. Clerics and Druids should max this.
Charisma: unless you're a Paladin, Bard, or Sorcerer this attribute does very little and only provides a bonus to a few of your skills, making it strictly inferior to intelligence. For Sorcerers, ensure you max it out. Bards and Paladins should have at least 14, preferably 16.

For some reason, Divination, Transmutation, and Enchantment wizards get away with only one opposition school in IWD2. If you're going to be a specialist wizard, pick one of these three. The opposition schools in these cases are evocation, necromancy and abjuration respectively. All three of these schools are easily discarded, so there doesn't appear to be any particular balance consideration here, and these are strictly superior to the other specialization options. Most of the good necromancy and abjuration spells can also be cast by Clerics, so it's really easy for wizards to get away without these spells if there's a Cleric in the party. There are plenty of damage-dealing transmutation and conjuration spells, so evocation spells like fireball aren't necessary and there just aren't enough utility spells in this school to redeem it. It's easily discarded. I wouldn't bother with Maximized Attacks, period. The damage boost just isn't significant enough for a once-per-day ability that requires you to get weapon specialization in two weapon types. It will still be noticable, but it'll definitely be more manageable once you've got a few levels under your belt.