Personally, I think at least 3-4 pics per category (maybe 1-2 for preg and death and a little more for profile) is a good place to start, though it's not really a hard minimum. More is better, obviously, but to me, quality comes first, and I'd rather see a smaller number of good pics than to have to look at a not-so-good one every once in a while.
As for design differences between uniques and randoms... With randoms, you should take advantage of the fact that the stats are randomized, while still making sure that your girl type has its own distinct character. Give them a small number of guaranteed traits (or near-guaranteed, as in 80-90%) and a few uncommon traits (30-50%) to define them as a group, and a large number of rare traits (5% or less) so there are still different individuals within that group. And for the stats, settle on which are important for the girl type, and set them to minimal variation; the others should vary widely.
Like, say you're building a soldier girl. For the stats, you need constitution and combat skill, and you want to set them pretty high, maybe at 75-95. Agility is important, but you can have the slow, strong type, so set it to 30-70. Everything else can be 10-60 so you can have smart ones, dumb ones, cute ones, etc. As for the traits, you can have strong and tough at 75%, you can assume many will be scarred up so you put small scars at 85, cool scars at 50 and horrific scars at 20, and some of them will be assassins or adventurers, so you can put those at 25. That said, this is the group, and you want individuals. To get individuals, you set up a bunch of 5-10% traits, enough that each one is rare, but the girl is almost guaranteed to have a couple. That's where you go nuts with the nipples, breast size, legs, figure and other physical or personality traits that don't directly relate to being a soldier. And in the end, maybe some of them got traumatized or hurt in the war, so put in fragile, mind fucked, twisted, one-eyed, sadistic, maybe even some addictions, all at 2-5%.
So in the end, you have your soldier girl type, which is defined by high combat and constitution and the tendency to have scars, and among that type you have interesting variations in body type and personality, rather than every soldier girl being a clone of the other.