One thing to make sure is that you use a paint that is made for
lexan/polycarbonate. If you use normal paints, you may find that your
nice paint job starts to flake off due to the flexing of the body.
Since you paint the inside of the body, dark colours go on first!
You don't need expensive compressors or air brushes unless you're
going to be doing complex paint jobs where you blend paints and other
effects. The spray cans, masking tape, is generally all you need.
Before you paint, you need to determine if the body has an outer
covering. If it does, you don't have to cover the outside of the body
before spaying, but make sure you remove it after painting and before
you put the sickers on!
Tamiya.com have an excellent range of 1:10th scale lexan bodies. They
are very realistic. Kyosho.com are also quite detailed. hpiracing.com
also make some nice bodies, but they are designed more for performace,
and aren't quite as detailed or correct as Tamiya or Kyosho (this also
goes for most other body makers).
Tamiya sell pretty much all you need for painting the bodies. Their
products are excellent quality, but they are on the pricier side.
Some guides for painting:
The "Reader's Rides" column has some nice paint jobs: