I'm sorry about answering that late, i completly forgot to...
to use shading is boring and steel time, that's right.
BUT it makes the vehicles much better and is pakset-standard, so you see instandly if one of the vehicles won't use it.
it's same with anti aliasing - you'll invest much time, but you get a much better vehicle.
i'm using GIMP ('couse it was on my computer
), but i guess for beginners "aseprite" will be a better choice.