Let me give a try.

1. Color is personal. As long as you like it. But you want to sell your house late on, it might choose a color apealing most people, e.g. antique white, cream brown, etc.

2. White (e.g. simply white or antique white) is very trendy now for doors, base boards, door and window casings.

3. A. Use 150 sand paper to sand the old paint.
B. Prime it.
C. Use 220 sand paper to slightly sand th primed board.
D. Choose good quality paint, e.g. benjamin moore. Buy good paint brush and roller. I would suggest to use Latex semi gloss paint. In this case, you can add floetrol to allow paint to dry slow so that you have more time to work on. Use small size brush work on detail at first. Then use roller to roll large surface and immediately use brush to smooth out.
4. Use tack cloth.