Well I went to art school, but I usually hire artists for my games (or have art provided when I was working at studios). I did a few minimal amount of art work on my demos, mostly just customizing textures, and modelling simple stuff like the walls and floors.
You are correct, it will increase the size of the game if you combine the sprites. It will also get tricky if you have a lot of enemies with different colors or clothing, and you would have to make a lot of different animations. But there are ways to do it with 2 sprites as well. It's just about snapping the second sprite to the right position and syncing the animations.
