Krylon Fusion is a spray paint made for plastic, you can find it in many hardware stores walmart etc. It is good stuff and quite forgiving, I have been kind of sloppy a few times and expected drips but it came out perfect.
Future over the top of a paint job does do a nice job of making a smooth finish, I have had a few paint jobs that were not as good as I had hoped but Future does a good job of filling in low spots or evening out orange peel.
I like to let the paint cure for a few days then I put it on straight from the bottle with a brush but most recommend spraying it. For spraying I think you can thin it with water, or use it full strength. For clean up use an ammonia based window cleaner like windex. You can also use this to strip it if you don't like it.