I have a good friend who is a gilder by trade, and have watched him do many a job with both oil and water gilding (mostly with gold but occasionally silver or copper leaf). We have often talked about the idea of applying leaf to a bike frame, but I've never had one I thought was appropriate, yet. One thing I have observed: he spends a tremendous amount of time preparing the surface: it must be strictly smooth if you want a smooth finish, so no "roughening" is called for. Once the (gold) leaf is applied it can be left as-is for a matte effect or burnished with agate-tipped tools to become really shiny. He has left some copper leafed objects un-varnished so they would develop a natural patina over time, but generally all non-gold leafing must be protected with a clear coat to protect against corrosion...gold will not corrode, but if it's on a wear-area protection would be advisable.
And as for tips (obscure pun) the thin brush a gilder uses to apply the leaf is called a gilder's "tip", and like a lot of things, using the proper tools will do a lot to make the job easier and the results more professional...but there is that investment thing.
Hey, BTW, GREAT bunch of bikes!