I love using stainless steel because I have always hated rust and especially when used for dropouts, fork crowns and brake bridges. It means your paintwork doesn’t get damaged. I found out how to polish it up from the instructions given by Darrell McCulloch of Llewellyn bikes fame and you could have done no better than reading his instructional piece on the framebuilding collective website. Unfortunately this organisation is defunct so we continue to hope it may appear elsewhere one day.
I used to polish the parts after completing the frame but, as McCulloch, I now file and sand the parts to at least 240 grit emery paper before building the frames. It is much easier to get in all the recesses before the frame is assembled.