[RWebb]

use a high quality paint - it is all labor (well, 97%) so you don't want to do it 2x -- your experience painting cars tells you this; I use Benjie Moore and I use their best primer & one down from their best top coat paint.

a disc grinder works great for the sanding

a sprayer just puts the paint up there - you need to work in with pressure from a brush and/or roller

oh yeh - I don't just use a pressure washer - I get in there and scrub the old surface with a hard bristle brush too (why make it easy on yourself when you can indulge in a Puritan-like ritual of sanctification)