With regards to the brakes. There aren't too many. Usually bigger rotors stop more. They're are aggressive 12/13" rotors available from Brembo or like the custom ones from Wilwood I have. You could check out the the part# for the Supra Brakes and see if match your SC4, since they vary from year to year. When I was upgrading mine. the fronts were similar to the ones on the LS400, but the rears were closer to the Supra. Still needed to be modified with spacers. Now that's the proper way.
There are some Cross-Drilled or Slotted rotors on Ebay that will be better than the stock setup. You just have to remember the pads Carbon-ceramic are a bit more aggressive than the OEMs, but you won't need to resurface the rotors that much. Also, consider changing the Brake fluid. Motul, Redline, or Royal Purple work very well with aftermarket brakes.
That should help with your brakes.