The MMM esc comes bare, you add the connector you want, in your case a TRX connector to go with your batts. Yes, you want to run them in series. You'll also need a Castle link - MMM comes with auto lipo set to on and you need to disable it to run NiMh. You'll want the link anyway for fine tuning.

Castle is coming out with a field programming card "early this year" but I don't know then thats going to be.

I would use the same gearing as the Brushless version EMaxx is running. There is diff gearing based on the voltage that you're running - Here's the chart - they use 17/68 for NiMh -

http://www.traxxas.com/products/elec...peed_chart.jpg