I am converting my slayer to direct drive brushless and thought I had my battery issues figured out, but am now second guessing myself.

What I have is stock slayer w/ 1/8 buggy tires
mm with two caps.
medusa 60mm/3100kv
15t and 18t pinions 36t spur
2 speed intact and using mech. brakes

I figured it out for 3s packs, but now am am thinking of 4s or 2s packs in series. The thing I am worrying about is amp draw.
I was looking at 3s 5000mah 20c and 2s 4000 25c batts. Both should handle 100amps cont, but is that enough?

If it helps the roller with just servos and rx is 5-6lbs.