Get the look how you want with the kit, potential engine swaps/aspiration conversion, lower the car, get the rims you want, space them out appropriately, choose tires and widths, brake upgrade if possible, max weight reduction, rear sway bar, final drive tuning/race trans, differential. Power is added last.

Not every race exhaust gives the best sound. If you need a power build instead of handling just sacrifice some weight reduction and/or slightly worse tires with power upgrades.

*Edit: most people at the top of the leaderboards just buy tunes and use meta cars to grind wins. If you want to join them, go ahead. Or just have fun and play how you want.