1)I would not bother with a flight plan for that. You can be in radio contact in case of emergencies for the entire flight
2)Perrenporth is really relaxed, just give them a quick call before going, they can give you a few hints before the trip. Just watch the runway, it is a touch bumpy! (and noise abatement)
3)Just book out for a land –away. Again it will be the usual (call-sign, A/C type, POB, destination etc)
4) Last time I flew there from your area I routed to the BCN VOR then outbound to overhead Swansea then over the water to Illfracombe, across Bideford bay avoiding the Chivenor ATZ and danger area, then down the coast to Perrenporth.
On that route I would probably speak to Cardiff lower airspace radar service (LARS) once in range, Swansea and then London information once half way over the water, St. Mawgan radar then finally Perrenporth. Generally as VFR traffic in the u.k. you will not be passed on. Each call will probably be from scratch. And yes, it is good to talk.
5) Three types of basic service in the U.K. For you I would suggest either ask for a ‘Flight information service’ (FIS) and possibly a ‘Radar Information Service’ (RIS) from Cardiff and St. Mawgan. A FIS means that you are given information about other known traffic and as with all the services, an alerting service. A RIS requires you to be identified on radar, and then you are given information about other traffic based on radar traffic. Obviously to get a RIS you need to be in contact with a unit with radar. Radar advisory and Radar control are the other types, not really applicable. I would suggest a read of CAP 413 which can be downloaded for free from the CAA web-site.
6) Last time I flew down from the north St. Mawgan gave me a RIS and asked me to call EGTP field in sight. Once in sight I was asked to ‘Free-call Perrenporth’ i.e. they did not pass my details on.
7) Yeah, watch the runways, they are bumpy. A great place to visit though, a really friendly airfield.
Edit: And here is the link
RT manual