I always build up a bicycle and ride it before starting to spend money, time and effort on cosmetic issues. You will be sorry if you do the cosmetics only to find out that the frame or fork set is bent, or that you don't like the ride quality of the bicycle, to begin with.

Once satisfied that the bicycle frame's integrity is not compromised, then think about painting the bicycle. Do not make the mistakes I made when I built up my first vintage road bicycle, a mid seventies entry level Sekine that I called "Big Green".