Another thing to consider is having 'twisted' versions of the normal races too; don't limit yourself to only normal races. Life in near-total or total darkness is a pretty big evolutionary pressure in the real-world, and creatures that are cave dwellers look kinda creepy to us. If we find non-magical cave dwellers creepy, imagine how they might be in a world where magic exists, so go for some horror factor in your monster choices. By the way, most creatures will be blind and albino in areas without light, and may only have vestigial eyes that don't exactly function except as a general light-level sensor, and there may be several types of sentient beings off the same basic type, if enough generations have passed since they last saw light. This makes having normally functioning eyes a dual-edged sword, especially as most enemies will have tremorsense or something mechanically similar. Tremorsense or something approximating echolocation is probably the best way to go about it, as that's the way most real cave-dwelling organisms 'see'. In most cases, where there is light, there will be light 24/7, but it will generally be like the last part of the twilight hours just before it really gets dark.. enough to see by, but not enough to see well.
All in all, this means dwarves and drow get BIG boosts to relative power, as their cool "I can see in the dark!" abilities are usually working for them in a big way, and the drow penalty to sight in daylight's almost a non-issue. I'd consider it strong enough to pump regular dwarves up to LA+1 at the least, since they're already very tipsy LA+0s in normal situations. One way to balance the darkvision issue is to make it spoilable by light.. and require a fade-in time to activate. Don't make it long, 1 round should be enough. This would mean those who don't have darkvision have a round or two to bolt before the darkvision renders them at a disadvantage. Spells with the Light and Darkness descriptors could be moved to higher levels or mostly removed, to drive home the fact that light's something important. (I don't know how to deal with the drow's racial darkness SLA.. that's one of the defining abilities associated with drow.. I mean they're a OK baddie but they already kinda suck for LA+2 for PCs, so removing it entirely wouldn't be a good idea unless you maybe lowered them to LA+1) Personally, if I was going to do the campaign, I'd get rid of drow and just make the only elves normal ones, despite the drow being iconic for this type of environment. That's just me, though. Too much real-world in my fantasy I guess. If you really want drow, IMO, just make them normal elves mechanically, but dark skinned, paranoid, racist Lolth-worshippers flavor-wise.
If it's hard to find food and/or safe shelter, societies will be far far more paranoid about who they take in, and this is a good reason to have the drow society be the way it is.. plus it makes the idea that pirates are exiled members of the various kingdoms of the Sunless Sea, and that the reason pirates band together is simply mutual protection and that raiding is something they do to survive. Plus, it's kinda cool to announce death by exile... Slavery's also likely to be common, since excavation's back-breaking work and cave-ins will be common and dangerous. Thus, drow are a good model for ALL of the kingdoms, even the 'good-aligned' ones. Goodalignment in that regard might mean you only take captives in war as slaves.. or that you have strict rules on how to keep the population from over-expanding. (Yes, this could present another reason why people are exiled..)
Other fun things to note: big caves are cold and wet places, mostly. Staying warm and dry is a real consideration, as you don't want to become hypothermic. The bigger ones can get you lost very easily, too, as the rock dissolves in uneven ways, making tunnels that go nowhere, or branch off and reconnect.. a cavern the size of a large sea or small ocean will have a lot of little boltholes that will probably remain unexplored by sentient beings. Any ability that means players always know their direction is a very valuable ability, since it makes exploring a lot safer. If you're gonna make navigation important, beware.
One of the fun thematic elements you could do though is that making undead could be a good-aligned practice in such an environment as undead require no rest, food, or safe drinking water, and as such provide a useful means of powering ships that use oars for societies that do not wish to use slavery. Retcon the alignment of non-intelligent undead to neutral and remove the evil descriptor for spells involving raising undead and manipulation of negative energy and likewise removing the good descriptor for spells involving healind and manipulation of positive energy and the flavor of a death priest who raises dead can significantly change.
BTW, I really love the idea of a general human/orc alliance, and I'd even throw in kobolds with the orcs. I am also in favor of keeping with the older flavor of having the orcs be lawful and regimented. I would think making the orcs/kobolds and drow be skewed reflections of one another, with differing racial tendencies in terms of class choices but making the kobolds and orcs more likely to favor physical fighting over magical attack and more prone to using mechanical equipment to aid combat. This gives you essentially an environment where the primary alignment conflict is law/chaos, instead of good/evil.
