I agree with not having him next to you all the time but the deal with the aircraft sounds good. Don't worry about not doing the 150hr course because you will need a **** load more hours after your cpl/fatpl before you get a job anyway.
I built my hours in a similar way and it was great as once trusted with the aircraft I had to make my own decisions to go or not to go as it was not at a flying school. If I was really unsure I would phone a friend (18000hr friend) and discuss it with him.
Go for it, its so much better than being tied to a flying school, you will see near the end when you will have to go to one. Don't worry about converting to another type either it makes no odds what you are flying now.
Enjoy