quick question.
with the clear coat, is it best to spray layer by layer or flood it?
With the colour spray several light coats, and only spray as much as you have to to get the colour even. The more coats you spray the darker it will get (Not that that's really a problem with straight black). Let it dry for a couple of hours before painting the clear coat.
With the clear, practice on a piece of cardboard first, you want to try and spray it on as heavily as you can without it running. Don't let it dry completely before spraying the next coat (ie. wet on wet coats as much as you can without it running). Got nuts with the clear coat, too many coats is better than not enough.
Once you're satisfied let it dry properly for at least 24hrs. before attempting to polish, otherwise you run the risk of polishing the paint straight off.
Like I say practice first on some cardboard otherwise the thinners or sandpaper will have to come out. If you do get a run in the final coat or two, it is possible to CAREFULLY wet & dry it out with some 1200 or more grit, using a sanding block & the paper wet, so that you only sand the run & not the rest of the paint.
There is no need to sand between any of the coats. Maybe you could lightly sand between colour & clear, being particularly careful you don't take off all the paint you just put on, but if you do, make sure it's cleaned up very well afterwards so that you don't get dust in the clear coat. Personally I haven't bothered sanding between coats and have had good results.
Check out this thread, for a little DIY on did when I colour coded my wife's Skoda grill to black magic...
http://www.vwwatercooled.org.au/newforum/upload/showpost.php?p=164539&postcount=4