Emaxx 3905 gearing ?

So I have an Emaxx and a Medusa 36-60-2000 v2 coming. I don't have a clue where to start my gearing.Could someone give me any ideas,PLEASE?I'll be running with a mmesc and 4s,till I can get a mmm.I'd love to buy everything from 15-25,but at 12 bucks a piece that would get a little costly.I'm looking for 40+ mph and usually don't run in thick grass.