Servo: Ti gears and 200 in/ozs + of torque. speed is nice, but the most popular steering servo is probably the Hitec 7955 (333 in/oz @ 6v). Budget choices would be the Savox 1256tg (277 @ 6v) or (ahem), the Hobbico CS170 (essentially a re-badged Hitec 5955, the predecessor of the 7955). All of those servos are around .15 in speed. With the Savox, Just spend the extra 5 bucks for a glitch buster. They like their electron coctails...a whole lot.

Power: Personal experience. Castle Mamba Monster Max Esc. Not the Mamba Max Pro. The MMM is Damn near bullet proof. Tekin's RX8 is a great performer, though is not quite as reliable as the Castle MMM. I've used both, the tekin is marginally smoother of the bottom, but it switches to sensorless once rolling...

I like Tekin Motors. Make sure you purchase the cans designed for buggies and really, the 1700kv motor geared right and on 4 cells is plenty of power. Plenty.

Purchase mod1 pinions between 14 and 17t. Purchase a 44t spur. With these gears you can pretty much get your gearing right, no matter how big a track may be.

Good luck, you picked a great chassis.

*disclaimer: I'm not an expert. Not even a Professional in the field. Just research and experiment well.