If ya not gettin insured on ya parents car & goin straight for one of your own, get a small engined car, Fiesta, Corsa, etc
so it dont break ya bank, then ya can build up ya no claims discounts over the years and move on to bigger and better cars
First mod, its entirely down to you, style your car the way YOU want it to look, not what other people think it should look like.
Most people change the wheels first on the exterior. 6*9's and a CD headunit are usually a good starting point for interior mods
Whatever you choose to do, keep us updated