The cars are wickedly fast stock - drive it a while and see what ya think.
THEN make performance mods as required by your results.
Pick up some nice outer and interior mods like colored or stainless or chromed lettering, painted calipers, new rotors(drilled and slotted maybe), rims and tires, tigershark nose, tint, Z06 screens and rear brake ducts, etc
For the engine, easy bolt on mods can be a catback exhaust, new airfilter(K&N or replace the whole thing with a Ramair or Breathless airbox. Can replace the stock airbridge and collar easy too.
After that, ya get serious into heads and tuning and custom headers, and the like. $$$$$
Interior stuff like custom colored sets, center arm rest, shift boot, cup holders, lloyds floor mats, aluminum guage cluster frames, replace your LED lights under the panels with newer, brighter, colored LEDs, and more.
THen you can move on to the engine dress up kits.. custom painted or carbon fiber or chromed/billet engine cover pieces, hood inserts, etc etc etc
it never ends!!!!
Rain hehehe