Welcome to the group, and i have to say that is a great car to have as your first car!
I would definitely not be lowering it, or changing the exhaust for one the size of a small tunnel !
Larger Merc wheels would look good ( price of tyres will increase though ) ....
Definitely lots of polishing, detailing and general looking after will certainly make the car look great .....
But i am not 17 ..... But had this when i was 20 !! Vert tasteful and understated ...... NOT! And yes it did have two scaffold poles as an exhaust system !! What a great way to stay single