I'd wait together the washers until your strings arrive so you can get the right size. Just take the current plastic one to a hardware store and match that to a metal one.
As for fingerboard wear; it's inevitable on any fretless. Many fretless' have a polyurethane or epoxy coating, but those will also need touching up after a few years. There are a number of oils that some players use, but 100% pure rung oil is one of the only ones that's really easy to apply and adds actually polymerizes to a slightly harder wearing finish.
I'm assuming your iphone thought it knew better than you, and I should wait to get the washers, not wait together the washers. Do you think fingerboard wear will affect the playability of the instrument? Or just the aesthetics? What coating do you/everyone think is best? Or maybe none at all?
