Glad you made the choices.
Pinion. well, I use a 7.5 and normally a 19/20/21 pinion....
I would get a couple to start with, maybe a 19 and 21.
as mentioned the steel ones are better, there only about £4.00 each so cheap to get a few for gearing changes. Tighter tracks need the lower pinion(shrccc) and larger ones(torch) need a larger one....
Good luck with the build........
