You are on the best plan, visit local clubs, Taplow (new venue) in Slough and DMS in Watford, there is also another club in Watford:
http://hertfordshirerccc.webs.com/ run outside on Sundays I believe.
Of course DMS also have one of the best shops in the country, (catchyerlaterDarren)
You will find the speed controls we use do not have reverse at this level, forward & brake mostly, takes some getting used to when starting for younger drivers, the cars are much faster than you may expect, advantage of the B4 is everybody in the sport has had one, fixed one and a good chance you may get spare parts trackside or quickly, they can be converted to mid motor(X6) if you are inclined. What about a B4 RTR and a B4 kit, upgrade the kit as and when. There is second hand stuff around as well. (B4 is Associated = imperial tools)