At this point I would suggest getting some wet/dry sandpaper used wet to get all surfaces smooth and to give the plastic some "key" (so it sticks).
Wash it with some soapy water, then you should be ready for primer. Tamiya fine primer is good (use white for light colours). Spray the primer wait a few days then lightly sand it down with wet/dry. It should be super smooth at this point.
For the best finish spray is the way to go, airbrush would be best but cans are ok. Use even passes, and right now in cold weather I would warm the can in hot (not boiling) water for a minute or two before spraying.
If you want you can polish it after it hardens after a week or so. Meguiars Scratch X is pretty good.
Good luck and post pictures
