1. Build the bike so it suits you. If you don't want to ride it, what's the point?
2. While some old parts look cool and keep the vintage "feel," some parts were utter crap even when they were made i.e. I don't think anyone here is an overwhelming fan of Shimano 555 hubs.
3. Keep the parts you take off. You might find another use for them, or you might want to trade later. Something that doesn't work on this bike will work on your next vintage ride. (or the next one, or the next one...)
4. Vintage cred for new parts hinges entirely on whether or not you put a Brooks saddle on your ride, even if the correct vintage piece was plastic.
