Brushless setups. HELP!

[portyansky]

For mechanical brakes you can use a Y-harness and disable the brakes on the esc.
As far as your motor/batt combo, well thats tottaly up to you. I also have done a crap load of research (Converting a Revo, waiting on parts), and found that for me the best range is 30,000rpm (came to this conclussion watching my friends).
Bigger cell battery, lower kv motor is your best bet.
Medusa motors seem to be holding up pretty well and are gaining popularity. They are not overpriced and a few have claimed even ran cooler then Neu motors. Not trying to talk you out of the Neu, just giving you another option.
My buddies have been running their MMM v2 for a couple months and no issues. Most (not all) people whos esc's have been "failing" is user error.
And if it does happen to fail, Castle is really good if it comes down to it.

1515 1Y is 2200kv, I would imagine 40,000 rpm in a truggy will be more then enough (unless you are bashing and just want to be nutso fast).
So a 5c lipo would be your best bet, 18.5 x 2200 = 40700rpm. You will be surprised who fast you will be.

Hyperion is a very good charger. The duo will require a 12v power supply, but if you plan on charging your batts at the track with your car battery it wouldnt matter, but i like to go to the tracks with charged batts.
If you dont need to charge 2 batts at once the Hyperion EOS0606i is AC/DC.

Steering servo, excellent choice.
LPR's all the way.

I hope I answered your questions, i dont know much about the gearing you should run, but maybe someone else will chime in.