Painting questions

I will be painting my mobile home, metal shed, wooden shed and wooden porch. The house is white with dark green trim and the porch and metal shed are painted dark green. The porch and metal shed were just power washed. There is also the cement surround and steps to paint. The porch looked kind of ratty, I guess. I like it, it looked rustic. I don't know what kind of paint was used on anything. What kind of paint should I use? Does everything need to be primed? I would like the dark green to be light green but I was told it wouldn't cover well enough. If I left the house trim ( which is a strip at the top and bottom) dark green, would it look goofy to paint the sheds and porch a light green?

Well that was long enough, wasn't it? Any suggestions?