As rough guide I'd look to: Sand the part using 120 grit (depending on the 'texture' you may be able to start with 240, or you may have to go for 80), then using a flat block work through the grits to about 400 and fill any flat spots that might've developed. Clean the panel and spray one/two coats of high build primer and you may have to sand with 400 grit and reprime any defects. Then flat the panel with 800 grit. Again every time you apply paint wipe the panel down and make sure your in the least dusty environment possible. Then apply colour coats, if it's metallic you must go to clear, if it's solid you can sand any imperfections using 1200 grit and recoat again and again and sand to get it perfectly flat. Then apply lacquer, several coats then wet sand 1200 grit, 1500 grit and 2500 grit before moving through the polishing compounds like G3 or use the 3M setup.
Thing is (especially so when your an amateur) most of the work in painting is the prep and not the actual painting, because if your really talented you can skip a lot of the final sanding stages if you get a great finish out of the gun and the you'll do very little (if any) sanding of coats because you'll manage to lay the paint on without orange peel or runs etc. Having said that even if your in less than optimal conditions with and have minimal tools you can get pro results but the trade off is lot's of time invested!!!