If you have properly isolated the motor and installed the brass weights (mass = density = reduction in plinth resonance and transfer of vibration), then you have accomplished 95% of the potential improvements available to your turntable. The next step is to purchase a round turntable belt. The pro-ject belt is flat, and a round belt is thick and has less surface area to transfer vibration to the subplatter. Then purchase a heavier Pro-ject counterweight (120g) and a pair of Herbie's Audio PTFE tonearm damping instruments. The belt, counterweight and damping instruments will cost under $70. Then you need to buy some records and enjoy your system.
Cheers.
Cheers.