You can fly an ‘N’ reg. using your CAA licence as long as you fly day VFR in UK airspace only! You are NOT aloud to ferry it into the UK without a FAA licence.
You need to register the a/c to a FAA approved trust (min 350 p.a), a radio licence for the a/c and one for yourself ($50). You are correct to say that if you want to put it on the ‘G’ reg you need an export CoA (~£800?). Survey the a/c and make sure that all AD’s are complied with, some can be very expansive! If you put it on the ‘G’ reg you probably want to use the PFA, so why not give them a call and ask the questions about the transition? Than you can make a better decision, a PFA route might be cheaper than ‘N’ reg.
Good luck