I would not worry about the instructor, if he/she has now passed then s/he's fine - as long as s/he keeps high standards. It may well have been rumours from jealous staff from another school trying to steer you their way.
Edinburgh would be good for you, less travel = less stress. Closer to your home = you can get there at the drop of a hat.
Cumbernauld is only a few minutes away from Edinburgh and the zone entry/exit procedure will be good pratice for you.
I have no doubt that you could complete the PPL in say two months. If you complete all the PPL exams and can fly frequently then you'll be fine.