at least a 35t. it'll be fast than you can walk, and have plenty of torque for climbing.

as for esc holmes hobby brxl if you want the best out there,and you can get it water proofed.
you mentioned lipo one day, so what ever you get, make sure it has a lipo cut off in it.
anything castle or castle based.
i got 2 AE-2's,1 in a cc01 and 1 in a tuber both on 2s
a mamba micro pro in my scx10 blazer on 2s
a 1st gen sidewinder in my 6x6 running dual 65t motors on 3s
and a losi msc12L in my creeper safari. it has a crawler mode and cut off for 2s

the holmes brxl is castle based as well