Welcome to the group!
My two cents worth , and it’s subjective, but you might want to consider a high torque motor and a 16:1 ratio gear set instead of a high speed motor. Keeps the motor temp down on repeated burst and sustained rapid fire, you’re grip won’t get so hot when you’re emptying out that HUGE mag go check out Galapogas J on Youtube, he has a great vid on high speed vs high torque motors.
Very good advice from Torc about the second gearbox… agree 100%. It’s always good to have a working unit to use while you tinker and learn about upgrades on the second one. Nylon gearboxes come in at around $45 online, so pretty cheap. Then if things go south with your upgrades you can still get out there and spray.
Other than the tappet upgrades Torc’s suggested, you pretty much have it covered. If you up your ROF substantially, you may want to consider a delay chip on the sector gear too… helps with feeding issues, and cheap as chips (sorry, bad pun) on ebay or any blaster outlet.
Most of all, have fun with it.