Start with the brakes you find the limits of these before anything else.
GT3 Brake cooling Ducts front and rear and high temp brake fluid, Castrol SRF or Motul RBF660, both are very cost effective upgrades.
Decent pads will help further, Pagid RS42 are good dual use pad. RS29 are over kill unless your spending circa 70% of your car usage time on track.
Tyres and suspension would follow, what you do depends on how deep you wish to venture down the rabbit hole!
The standard suspension has limited adjustability, but a geo will confirm that it's all pointing in the right direction.
Lose weight where you can.
Dependent on how committed you are fitting a bucket seat make a significant difference versus sliding around on the standard leather arm chairs.