Have you sprayed before, if you have any experience spraying definatly use two pack paint.
Do you have a compresser and spray gun? If not go to a "proper" paint supplier (not halfords) and get the right paint and get them to put it in the cans with the funny nozzle thing on the end. You get a much more uniform spray and it sprays in a line rather than a circle so you get a much precise overlay on the paint.
Not sure if new plastics come primed but if not make sure you use some scotchbrite to key up the plastics and thoroughly clean. Then use a decent clear plastic primer, before using a normal primer on top. Keep rubbing it down after everyother layer with P800-1000 until it is uniform all over. If any small holes use some putty/stopper to fill.
The main thing to say is to take your time, 100 thin layers will be better than 2 crap ones. So take your time and if you get any runs or imperfections, do not try and put more paint on, or blow it, touch it, or anything. Let it dry and lightly sand it down. Before spraying again. Only spray in the same direction, and try not to let the paint dry when spraying, overlap each line of spray to keep the paint wet underneath then you wont get any visible spray lines.
Once the surface is perfect then laquer it and hey presto!