What sort of quality is the existing paint & are you going to paint it the same colour? If Its not in good shape or you are going a new colour I'd reccomend primeing it first, if this is the case getting a compressor for half a day wont do obviously. If the bumpers are plastic and have cracks you really need to take it back to bare and use a plastic primer- otherwise it will crack easier sooner.
If staying the same colour you dont need to take all removable pannels off
- just stuff light lights, trim, door handles and door rubbers. some of these you can mask off but make sure you prep the areas around them properly otherwise the paint may flake.
When I paint cars I do any minor dent repairs, sanding with about 180 grit on these areas, then spot putty and sand with 400 grit. I then prime the car, sand with 600-800 grit untill glassy smooth- without going through the primer, then top coat.before the primer and topcoat also useing some prepsol or similar to make sure there are no wax deposits left. Depending on what type of paint you use, this can once dry and be sanded with 1500 wet dry, but thats really only with older acrylic lacquer's.
what type of paint do you plan to use?
3L will probably be enough, but i'd usually get 4l for that size just in case.
If you have never sprayed before than you will want to practice on something first just to get the spray pattern, overlap and other techniques sorted.
could also pay to go to your local library and have a read up.
As is always said with painting, prep is 90% of the job, the topcoat is nothing. prepare it good and the finish will be ok (generally). prep it bad and even if you are a master sprayer the finish wont be.
my 2.536cents
