Need help gearing brushless revo

[R00ST]

I never ran a REAL brushless in my emaxx (only the HV). so am not really sure how I would go about gearing a 7xl/9920 on 14 cells.

Also, is the mod1 really necessary? I dont usually dial in much slip (hoping with this setup its petty bulletproof, not too woried about the drivetrain, and I also dont do a whole lot of jumping)

It would just be a lot easier for me as I already have a whole slew of stock 32p spurs (66-72)
As of now my bill from you will be pretty hefty!
9920
7xl
motor clamp/heatsink
TF battery trays (hoping they come in!)
along with a few other possible finishing items.

& I still have to buy my new batteries (ouch!)