A coupla thngs, Mike, and if it sounds familiar after reading the threads that friend 73 referenced, so be it.
Nowhere on this thread have you mentioned SHOOTING this. All the gadgets and gimcracks on earth will not make up for a lack of practice.
Technology is a poor substitute for expertise. So is a checkbook.
Buy all the ammo you can afford. Cheap value pack stuff will do for now.
Shoot it at silohuettes,clays,tin cans,landfill rats,steel plates,old cars, anything, but shoot it until it feels like a body part.
Get the fit right, get your form down, and BA/UU/R until you're absolutely $%^&*()ing deadly. THEN, decide if there's a mod or addon needed to up performance or improve comfort.
BTW, one fast COF using a sling loaded with ammo will acquaint you with The Pendulum Effect and convince you that you've wasted money on something that downgrades performance.
(Dismounting from pulpit)...