Sounds like for your situation a lease would be the ideal option.
However, the conditions you listed (Mileage limit, unable to fully customize) are a few good reasons why leasing isnt always the best idea. That also includes scratches, dents, swirls, any imperfections on the car that has to be fixed and returned to close to showroom condition before you return the car, or you pay the amount that it fixes to cost. Also, if I remember correctly its 10 cents for every mile you go over your mileage limit. So you have to constantly keep your eye on the odometer. For me, leasing just takes away the freedom and enjoyment you should have with a car, you get too worried and concerned about the condition of the vehicle, how much you are driving it rather than actually enjoying it.
With that being said, if you do purchase and decide to modify the car, and decide you want something new, you can always return it to stock and do a trade in towards a newer Z, or whatever car you decide to get later on.
I would not worry that financing would hinder you from getting the latest car, remember new cars will always come out, so it becomes an endless game of cat and mouse. I say pick up a car you want, buy it, and don't look back. Afterwards, do what you want with it, and when the time comes, if you want, trade it in. Its better than having to deal with the restrictions of leasing imo.
