Engine
Tyres
Shocks,

In that order

Ive already done the engine, tyres, most of the Pro parts, and not gotta do shocks.

IMO the shocks that come with the Hyper are good, 16MM outside diamiter, 14.5MM inside.

But IMO the Hyper already handles like a cartoon, so a good engine would be the best choice. As you already have a bump box, get a Picco .28, $199 and it is a great motor. As for tyres + wheels, I run the wheels and tyres off my Pro kit ( Dog Bone Style ) and they are extremely good. The stock tyres are extremely grippy as well.