must be talking complete bolt carrier group, with bolt.
Yes IMHO all you need is a spec group. But how do you know its "spec"??? Best I do is buy brand name on that. And allow my smith to use his bolts when we rebarrel.
Chrome is not needed, though I have a couple coated with NP3 due to their rapid fire only use and the 27 hour drive I make to use them once a year... Can't afford a hang up.
Properly lubed bolt carrier will be fine.
I see no problem with a GOOD chrome coating either, but finding someone that hasn't just slapped it one could be interesting. Much like finding a TRUE mil spec group for 105.