Depends what you want for your car. Performance of looks. If your spending 2000 on a headunit but want replica wheels i would spend 700 on a decent headunit and buy 2300 dollar wheels. Or if money is no factor get both.

If you get a sub you need an amp i have not found one factory amp capable of running a good sub.

If you want performance start with intake headers and exhaust. But if you planning turbo dont worry about headers as you will need a turbo manifold made up etc.

Its all up to you