A good set of battery packs is essential. I like the SMC packs. The 4600's work good for my 4 cell 12th scale and the 4000 Li-Po works good for my touring car.
Touring cars in general don't have alot of room to put all of your electronics in. I would suggest getting a Low-Profile servo, and a micro reciever. This will leave you with a bit of room to put balancing weight, run a larger speed control, or tuck wires.