First off, 5 turn motor in a B4 is a really bad idea!
All it will do its spin on the spot. Especially on our polished floor.
Your wanting a 8.5/7.5 maximum. Thats what I will be running.
As far as a radio I have a 3VCS for sale with a Spektrum Mod & Receiver
if thats of interest drop me a PM. I can bring it with me.
The B4, is a pretty good all around car, There will be normally a handfull of people running B4/B4.1's along with a few C4.1's. So you will always have spares to hand.
I think the most cost effective way to buy B4 parts is to buy a full car!, You can buy them for £60-£80 2nd hand.