I used just regular rubbing alcohol. The higher the percentage, the better. Use that and go over the surface for a while. Better yet, if you can pick up some 3M scuff pads, I'd use those along the surface first to break up and silicone particles, then use the alocohol. Even still, in most cases, the alcohol is enough to break up any time of Meguires, Armor All, STP, etc. silicone cleaners/protectants.
As far as coats are concerned, not too many and not too little. Don't overspray or else you'll get the awful "orange peel" effect. And if you don't spray enough, you'll see the old color. Whatever you do, keep the sprays even, you don't want a rippling surface effect either because you sprayed too much on one side and not enough on the other.
Once you're done with the spray paint, be sure to spray some clear laquor/coat on top to seal that in. 2-3 coats of clear is plenty Good luck and be sure to get us some before & after shots!
to take out the passenger side vents, all u do is open the glovebox and unscrew it. The drivers side, you have to unscrew the two at the bottom of that plastic thing that goes toward the floorboard, and pull. its clipped in after the screws. That should give u access to the vent, if not, u may have to take off the metal plate that is behind the plastic to get to the vent.
Krylon Fusion Ownz!!! The only thing you need clear coat w/ it is for more protection, it adds it's own clear when it's sprayed. You did a good job on that door piece. For my prep, I used some stuff from AutoZone called PrepAll, it works as good as rubbing alcohol, but it's more of a pain to use.