Upgrading my G&G TR16A3 with a m150 spring
 

I want to put a M150 spring in my G&G TR16A3 Top Tech and I was wondering if I needed to replace my gears and piston I know I need a new motor but I am hoping to keep my stock gears as I dont want to spend that much for all these upgrades.

keep them until they break.
As long as you're using a good high torque motor and 7.4 or 11.1v lipo, should pull it no problem

I bet my gears and piston are good enough anyway I only plan to fire in semi auto anyways and I will probably upgrade the rest of my internals in the future. But do you thing that my 9.6v 5000 mAh battery will be good enough I know that the Lipos will give me better trigger response but I am just wondering

A 7.4v lipo won't give you better trigger response
Because you're using large cells, they should definitely have enough amperage to pull that spring without a problem
And if you don't already have a mosfet installed, get one installed when you change your spring, otherwise you'll be melting your trigger contacts