Kayla - get the insurance sorted first. You should get a quote on a bonus accelerator scheme with an older relative on the policy as a named driver and a mileage limit of 5000 miles for approx £2800. Try Adrian Flux / Greenlight etc....

NOTE: Adding an extra driver that is older than you with no claim / convictions etc. actually reduces the policy quite a lot because the assumption is that they will also be driving the car at some point.

And 20K is too much to spend for your age I would reccomend a small turbo (later car) - you should get a good one for £15K