RE: Balance and Advice
I can't help on the specific battery recommendation because I usually recommend going with the largest that will fit. If you're racing you don't want to carry around any extra weight right? A TC-5 with brushless on your specific track and runtime will determine the minimum battery. The 5000 is about the largest that'll fit in where 6 subC cells were.
On the balancing , most people who balance recommend it and those who balance blindly every time recommend that. Your pack may never need balancing, but should at least be checked when new and then after 1 run, 5 runs, 10, then 20 or 30 and so on. Once a history is established , the need for balancing is real predictable (unless somethng go haywire with battery or car)
The short answer is no balancing doesn't have to be done, but it needs to be checked and is a simple as checking voltages of individual cells. The other short answer is that if a pack is kinda hokey then it may need balanced every time.