All good.
On the race around the prison, Turn everything on...wanted level, traffic and the like. Set the laps to about 4-5, and then everylap just make sure that you do a quicker lap than the last....so on the first lap make a .50sec lap and then just beat it, but not by much that way you can do a super doooper flying last lap.
The choice of car/motorbike dosen't matter, but i find Muscle car the most fun.
With that 1 race you should be able to level up easy.