A sensitive subject, but any weight issues shouldn't be much of a problem for a PPL Class 2 medical. Also learning in a 4 seater C172/PA28 rather than the C150/PA38 will resolve the aircraft weight limitation. The only thing with the larger aircraft is to budget a little more. This isn't much more expensive, but it is a little.
As for the theory exams, they aren't difficult. Read the relevant book and take the exam. I recommend the Air Pilot's Manuals - the ones the exam answer sheets are referenced to! If you fail an exam, learn from it and do it again.
Completing a PPL in 45 hours is easily possible if you
know the theory before the you fly the lesson. They say 50 - 60 hours is 'normal', whatever that is. Just don't
expect to do it in 45
By the way I envy anyone who will learn to fly in Scotland; much more beautiful scenery than most here will have endured
Good luck!
GW