lipos for 1/5 scale bl?
 

How big and how many c

As much as your budget will allow really.

5ht scale would be 8s minimum. 40-50c lipos, with at least 5000mah capacity. Likely a 10 or 12s setup with a low kv, large motor would be the best bet. That way you can run 2 5s or 6s packs in series. Hyperion has some 80-90c lipos, look like the best bet.