This post may seem very forward, for that I apologise.
EvilleJedi has already started with a Star Wars mod, and although you are free to do what you want, surely it would benefit you both if you signed up on his and added your input. Rather than you both carrying the same weight, why don't you share it together.
To your first question, without sounding too harsh, everything to do with colours and textures will be in the Textures folder. If you haven't seen that yet, might I suggest doing some smaller mods and modding before you throw yourself in at the deep end. My point here extends to your second and third questions too, as with most things, start small and work your way up, gradually getting bigger and more complex.
And for your last question, I'd say leave the third race out. Yes there were hundreds of other minor factions and militia, but the main conflict in the Star Wars universe is between the Rebels and the Empire. Unless you are going for another era, then there may be more sides, but the most popular time is from the original trilogy.
Link to the Star Wars Warlords forum. This is where EvilleJedi is based and has a strong community.
