Are you sure your siding is steel? Or is it Aluminum? If your siding were steel and had areas of bare steel, those areas would be terribly rusted. Steel or aluminum makes a big differece in how you prep the surface, and the primer you'll be using.
Being unsure where you are, I'm almost certain that your chances of painting anything outside this year are not good. Exterior painting should be done in most northern areas before October is over. After that, you have unreliable conditions and temperatures.
Take the time to check into the type of siding you have and type another post.