One thing i would say is....
Going on your mums insurance is illegal (unless your actually going to be using ur mums car on a part time basis), if you have a prang ur insurance company are not stupid, how any middle aged women have a GTT... they will investigate and you can find yourself driving without insurance and loose ur licence.
Insuring a GTT is never gonna be cheap at a young age, but a good tip.. Pass plus, putting your mum, +anybody else with a full clean licence for a long period of time will help (I have 4 people named on my insurance... they may drive my car, but if they dont my insurance is still valid + often cheaper)
Get a good alarm/imb, put it in a garage, keep mods senseible etc..
Oh and joining RTOC can lower your insurance.