Well, after having beaten the game once already, I decided to try my hand at utilizing some of the other classes just to get the feel for them. So in a new game here is the the party I've got:
1) Aasimar Paladin of Ilmater (to be later multi-classed with Painbearer of Ilmater, debating at whether to start him as Cleric after 3 or 8 levels of Paladin, the latter so I can utilize the Fiendslayer feat; meant as buffer/healer and tank/damage dealer)
2) Shield Dwarf Barbarian (planning to give him 4 fighter levels, possibly after level 20 if not before, so he can have Weapon Specialization and Maximized Attacks; meant as principle melee damage dealer; also my Intimidate expert)
3) Human Druid (primary healer and secondary magical damage dealer)
4) Human Rogue (will give him 4 fighter levels and 5 bard levels after 12 rogue levels and then go back to rogue from there; meant to be sneak attack & ranged damage dealer as well as use bardic instruments/Use Magic Device to fill in where needed, especially using Raging Winds in HoF mode to provide powerful backup)
5) Human Sorcerer (primary arcane damage dealer and chief Bluff/Diplomacy user)
6) Human (generalist) Wizard (will focus on buff and [especially in HoF mode] summoning arcane spells, but will learn every other spell via scrolls just in case)

Now, the druid in this case will focus on spellcasting, namely healing, druid buffs and damage-dealing spells. I don't know how useful druids are at crowd control, party since Entangle is not allowed to be cast in man-made settings. I know Druids get the Spike Stones spell but I've never used it myself before. Do they get any other useful spells to use for breaking up crowds of non-animal enemies?
Also, which feats are best for this one? I heard the Spell Penetration feats are bogus because enemies, namely in HoF mode, either have too much or too little spell resistance to make the investment worthwhile. Now, what feats are worthwhile? I'm thinking Combat Casting for emergency heals, and later on Spirit of Flame and Scion of Storms for damage spells. What about Spell Focus (Evocation) and it's upgrade? I hear all the Wild Shape feats except the Shambling Mound one are garbage.

Concerning Sorcerers, I know they rely on Charisma instead of Intelligence and cast a small selection of spells per spell level multiple times per day instead of memorizing several different spells per day. What spells and feats should I go with, due to their limited selection? Concerning spells, these are what had in mind per spell level:
1st - Magic Missile and Chromatic Orb
2nd - Melf's Acid Arrow and either Gedlee's Electric Loop or Aganazzar's Scorcher
3rd - Fireball and Lightning Bolt, maybe Skull Trap
4th - Mordenkainen's Force Missiles and either Shout or Vitriolic Sphere
5th - Sunfire and either Ball Lightning, Cloudkill, Phantom Blade or Shroud of Flame
6th - Chain Lightning and either Acid Fog, Acid Storm, Darts of Bone, Disintegrate, Soul Eater or Tenser's Transformation
7th - Delayed Blast Fireball and either Finger of Death, Malavon's Rage, Mordenkainen's Sword, or Prismatic Spray
8th - Horrid Wilting and either Fiery Cloud, Flaying or Great Shout
9th - Meteor Swarm and Wail of the Banshee; dunno about Black Blade of Disaster
As far as feats, I'm thinking Spell Focus in Evocation and Necromancy (and their upgrades) and - if possible - feats like Spirit of Flame, Scion of Storms and Aegis of Time.

How does that sound?

Looks good, although you might even consider multiclassing out of Paladin at 1st or 2nd level since the real Paladin goodies come at first. It's worth noting that this character will be stretched thin for attributes. Strength for melee, wisdom for cleric casting, charisma for Paladin class features, constitution to not-die, and at least passable dexterity for AC... even with a 3 in intelligence, something's going to have to give. Pretty standard, although I would note that Maximized Attacks is annoying due to being once per day. If you're the kind of player who rests after every combat it's not a big deal, but for a guy like me who tries to clear out entire dungeon levels between rests... a once-per-day feat is really underwhelming. Word of warning, healing only becomes decent once you get the Heal spell, which comes rather late for Druids. The lower-level healing spells are kinda trash that you only use outside of combat. Especially in HoF mode enemies deal so much damage that there's basically no point in casting these things in combat. Clerics get the convenience of spontaneous conversion, allowing you to prep useful low-level spells and still be able to convert them to heals if you need to top up between combat. Looks like a classic jack of all trades, master of none. To be honest, the Rogue was nerfed so harshly in IWD2 that I'm at a loss for any reason to ever take levels in the class. The cross-class skill system means that other classes can disarm traps and open locks now, and the reduced number of skills in IWD2 compared to D&D means a 6-man party can easily cover all of them without a Rogue. Then there's the nerf to his sneak attack ability, which leaves his damage output too low to provide meaningful assistance in combat. As I said, I'm at a loss for any reason why you would ever take a Rogue over something else. I'd say just get rid of the Rogue entirely and focus on Bard levels. The fighter multiclass will hurt his spellcasting, but if you want to do ranged damage support it'll be a big help. Sorcerers are awesome; easy addition to the party. Yup, only reason to go with generalist is if you really want to make sure you can learn everything. Given how stingy IWD2 is with scrolls, being guaranteed you can learn what little you find is really nice. Still, I do miss those extra spell slots. They're not as good as arcane casters in this regard, but they've still got decent options. The nice thing about prepared casters (as opposed to Sorcerers and Bards) is that you can just swap out spells if you decide you don't like them. The 50% damage boost feats are really nice if you're focusing on elemental damage. Spell Focus is necessary in HoF since saving throws get kind of insane. Sadly there's no Spell Focus (Conjuration), meaning all those awesome low-mid level Conjuration spells kinda go obsolete because you have no means to bolster their saves (although prior to HoF these spells are awesome). Spell Penetration is still helpful, since it's a pretty big boost in the chance to penetrate against enemies whose SR is competitive with your caster level. Looks a little heavy on damage-dealing spells. You don't really need too many of them, and IWD2 generally encourages elemental specialization with the +50% damage feats. Having a balance of buff, debuff, and utility spells to round out the damage-dealing ones can be very helpful. Sorcerers are a tad trickier than Wizards since you can't swap out a spell you find you rarely use. None of the spells you've listed are bad, but I'd wager that there will be at least a few on that list that you find you'll rarely use, but which ones will come down to your own personal preference.

Many druid spells are transmutation spells so GSF transmutation is also useful for them. Combat casting sounds great but only offers 4 skillpoints which might never make a difference during the game.

I like how you focus your sorcerer on offensive spells instead of adding cheesy pre-combat buffing and protection. Will be more challenging but also more fun this way.

Be aware that the most important stat for sneak attacks (and all other physical attacks) is strength.

Well, yes, I understand the importance of the Heal spell. My original party is currently in Chapter Four in HoF mode and all my Morninglord of Lathander casts for curing wounds are Heal and Mass Heal. Still that's where my Paladin will kick in. I know caster level checks improve beyond 20th level, but I only want to invest enough to get 9th-level spells. Plus,

As far as my Sorcerer's spell selection, I wasn't sure if I wanted to diversify his spell selection too much. Last thing I wanted to do was restrict his firepower too much and leave him gimped in a fight. After all, my Wizard is going to deal with buffs, debuffs and summons.

Now, my Paladin and Rogue have good enough scores. They have all 18s in their primary stats and I dumped their Constitution stat, only to console in enough Constitution options to bring said stat back up to 18. Call it cheating if you will, but I found out stuff from the shortcomings of my original party. As far as my Druid, I dumped her Charisma since 1) Animal Empathy is essentially useless, 2) my Paladin and Sorcerer are handling Diplomacy checks and 3) Druids otherwise don't use Charisma.

Sorcerers, unlike Wizards, can freely cast any spell they know. Therefor as long as you know a single offensive spell at the appropriate level, you can convert every remaining spell slot into offensive magic. This means Sorcerers don't need to know very many direct offensive spells. You might go for two on a specific spell level if you're worried about resistances or immunities and want to hedge your bets, but three or more on a single level is overkill. IWD2 is already very generous with stats, giving you enough points to max out three attributes with points left over. If you've "adjusted" your stats to max out a fourth for free, you're pretty close to a perfect spread.

Still, that won't really help the Rogue. The game is largely balanced on the presumption that you have an 18 in your primary combat stats, so he's not actually getting a leg-up as a result. I still think you're not really getting anything out of those Rogue levels. The class just... doesn't really do anything useful :-\

Well, when it comes to substituting the Rogue, I heard that Bards are worthwhile past 5th level. Is that true?

Yes, that's true. The level 11 song is also very useful in battle no matter which kinds of enemies you face, the level 7 and 9 songs aren't useless either and because of lingering song you can have 3 songs active permanently, making bards very useful party members even if they do nothing but singing.
Bards can summon and buff before a battle and heal afterwards. It's worth keeping them pure since their high level spells help more than the low level stuff you might get from other classes.

Oh, that was meant to be typed as "aren't worthwhile past 5th level". Now, if I were to have my Sorcerer keep up with Diplomacy and Bluff while my Wizard deals with Alchemy, Knowledge (Arcana) and Spellcraft, could a Bard deal with Rogue skills? I know Disable Device, Open Lock, and Search are cross-class skills for Bards.

Eh. The Bard class has some spare skill points, but they run on Charisma, not Intelligence, so you won't be getting much from their casting stat.

The Wizard handles Disable Device and Search better than the Bard, since a high intelligence score gives you a bonus to those skills.

I personally found Open Lock completely useless in my playthrough. My Half-Orc Barbarian was able to force open every lock I encountered through strength alone, though there were a handful he needed to enter a rage to open.

THIS DOOR MAKE HULK ANGRY!!

No items in chests can break because of that, right? I know there was a risk of such in Pen & Paper D&D as well as games like Neverwinter Nights 1 (unsure of such in NWN2) as well as at least one non-D&D game (Lands of Lore: The Throne of Chaos). I have played plenty of games to know that some actions run the risk of some form of disaster. :S