The desired finish and paint type will determine the final sanding grit. Always step up in small increments. 100-220-300-400-600-800-etc. If you are going with DuraTex textured type finishes, 220 is fine. 220-300 is fine for anything you plan to roll on. If you are looking for smooth finishes, either matte or gloss you really should finish with at least 400. The most durable finish you'll find in a rattle can is lacquer or polyurethane. They also tend to produce the best finish. Do not attempt to spray either of those on cold or humid days, they will blush. Black lacquer rattle can paint is readily available. If you cant find that, Minwax sells their fast drying polyurethane in rattle can and that produces a very good finish. It can be sprayed directly over flat black, wet on wet. Meaning once the black paint has dried to the touch, the poly can be sprayed on with no sanding. But do not wait more than an hour or so.
JVC RS-540, Sony UBP-X800, Onkyo TX-RZ730 (7.2.4), Onkyo M-5010, Elite Screens 100" 16:9 (Spandex AT DIY)
DIYSG 1099 LCR, Polk TSX-150C (DIY) Atmos, Yamaha NS333 Surround & Surround Back
Triple HS-24 mkiii sealed, Dual SAN 214.5 Devastators, Dual Crowson actuators, NU12000, NX6000, XLS-2502, MINIDSP 2X4