1) Not really, particularly if you will talk to agencies enroute.
2) Varies from place to place -- usually callsign, type, ETA, numebr on board is all that's required.
3) Same details as usual, plus destination.
4/5) LARS is the equivalent in many ways. See
ENR 1.6.3. (Register at
www.ais.org.uk if you haven't already.)
I would talk to any of Birmingham (not strictly a LARS provider but usually happy to help subject to workload), Brize, Filton, Bristol, Cardiff, Mawgan requesting a radar information service.
6) I doubt you'd need to talk to Culdrose. The AIAA you may be looking at does not require mandatory contact with Culdrose. Mawgan should look after you.