Plett Powered Hyper 7 TQ Sport Project

I'm in the middle of building my Plettenberg powered Hyper 7 TQ Sport, and I have a few questions.
1) I'm considering using the Ofna Dominator Center Slipper Drive instead of the differential that came with the kit, mainly because I can use a plastic gear instead of the hardened steel spur gear. What is the downside to not using the center diff?

2) I'm getting the Plett BigMAXXimum and would like to know which controller to get? Should I get the Schulze 18.97kw? I'm planning on using 16 cell Intellect 3800 packs.

3) If I use the 51T plastic spur gear, which pinion should I use?

Items already purchased:
Hyper 7 TQ Sport Kit
Center & Rear CVDs
F&R Aluminum Chassis Braces
JR DZ9000T Servo
JR XS3 Pro Radio
ProLine Badlands Tires