I can't speak to most of this but one thing I would suggest is since they are relatively small to dunk them in a small tin of Acetone to ensure they are completely clean. Swabbing sometimes just moves the gunk around and doesn't remove it.
As to the paint. These may be two small for this method, but you could think about painting a base of light grey and the taping it off and with a very sharp brand new razor blade "scrape" the tape off on the edge to be painted (it is easier show then described) and this leaves a nice edge on the stuff I have done, albeit, nothing this small?
