Doors – is 3/8 inch nap roller ok for painting a door

This article provides a pretty good run-down.

1. Yes you should clean: soap and water or any other mild cleaner is good.

2. You may not need additional primer, but you should fix any dents/scratches -- they will stick out after you put the new paint on. Auto-body filler (eg Bondo) works for dents and deep scratches. Before you prime, the whole door should be lightly sanded using 120-150 grit sandpaper to roughen the surface, and then wipe the whole door down to get rid of any particles from sanding.

3. Use an oil-base primer, and again, be sure to lightly sand first.

Sounds reasonable to out-source it, but you will still need to do a final coat on the casing after you install (door should be fine if you are careful).

To "do it right", you need to fill the nail holes and corner joints and sand, and then run a bead of painters caulk around the casing to make the cracks disappear, then paint again.

I just did the caulk on the inside (casing-to-jamb) not the outside (casing-to-wall), and didn't paint very far onto the side of the casing where it hits the wall. This way, you get a nice sharp line at the wall without a lot of hassle.