Others will embellish but 150 hours aeros per year is a lot - nice if you can afford it, but out of reach of most I would guess. Probably 5 - 10 hours or so on top of the basic AOPA aeros course will see you put up a decent showing at Basic level BUT it very much depends on how that training is spent. 10 hours at somewhere like White Waltham including some ground critique from an experienced competition pilot is worth 100 hours heaving a C152 around the local area with no guidance, and you could be ready on completing the course with no further training. If you want to enter competitions look at the BAeA website and go from there. Progress to Standard level is not too difficult once you are happy at Basic, but as to doing it well........
Good luck anyway.