Sleep 'requirements' are not specifically defined in 2nd Edition, only the effects that a lack of will have.

There is no "copy yourself ring" in BG2 and ToB unless it is a mod thing then I don't know. However, there is a helmet called Vhailor's Helm that allows you to cast Simulacrum and make a copy of yourself at 80% of your original level. I agree with the idead that with right armours and weapons fighters are 'easier' to play, but once you get familiar with the game mechanism you will find that spell casters are more powerful in terms of versatility and raw power. Let me ask you this question, have you tried playing a mage that does not use any weapon (not even range weapon) in BG2 and ToB? I have and the truth is, it is not as hard as you would think. Try doing that with a fighter and see how the fighter fares.

I am not saying that you don't need fighters in a party, what I am trying to say is, fighters and mages all have their uses in a party since BG is a party-based game.

Roll a fighter mage, problem solved. Guy can even solo everything. Why compare and contrast? Unite and wreak havoc.

I've always played fighter classes as the main player class in Baldurs Gate series because I really suck with the low hitpoints at low levels. The thing about "preparing spells" for a wizard in BG1 is that it usually involves a lot of load saving which I get tired of very quickly. At least with a fighter, at low levels, you can just walk in and hope to defeat the enemies whatever comes your way with a few healing potions and anti poison potions up your sleeve. A wizard that goes in with the wrong spells is usually followed by reloading the game...and fighting all the monsters that get respawned because you've reloaded the dungeon.

What about human dual-classing? Kensai-mage or Berserker-cleric?

Berserker-Mage is Best. Berserker has immunities which affords you to not waste arcane spells for similar purpose buffing. Getting it 13 level, allows you an extra, second attack per round. Getting it 13 level, also allows you to hit 28 mage, ergo you can have MAXIMUM slots in book for spell casting, as if it was a pure mage. The only downside is that you loose fighter HLAs (high level abilities), but a maxed second class mage makes them highly insignificant, if totally unneeded at best at all.

Kensai on the other hand, gets more damage, but doesn't have immunities, looses gauntlets too; and in ToB, there is a certain pair of gauntlets specially designed for fighters, which cries out to be worn on one. Kensai mage, for unknown and unfathomable reasons, are totally overrated. You HAVE to try a Berserker mage in order to become convinced first hand that it is superior.

Berserker Cleric, is another interesting class. Arguably falling a little short behind the all time classic, Ranger Cleric. Ranger cleric, is actually a kind of fighter (ranger), which gets all divine spells, cleric and druid included. Consider it instead.

Of course, at the end, you can and you should play the class YOU feel comfortable with, but those two beauties, Berserker Mage and Cleric Ranger, are both fun and overpowered. If you know the basics of each of their own, respective classes, then you can't go wrong while using either.