Richard
Welcome to PPRuNe. I think all of your questions have been asked before so do a search and you should be able to find the answers... hence why no one has yet replied to you.
eg
http://www.pprune.org/private-flying...-scotland.html
There are many great training locations around the central belt. It is competitive enough that most of the bad eggs don't stay around too long but to keep safe, don't pay up front (or if you do - use a credit card and don't spend money you can't afford to lose). I'm at Prestwick Flying Club which has a very different atmosphere to some of the more professional schools but it depends what you are looking for. I believe I'm learning a lot more about good airmanship from the commercial and ex-military pilots and instructors who frequent there than I would at a traditional commercial training school. I've also learnt about care of the aircraft and individual aircraft foibles which you would expect to be hidden from you at a commercial school.
Remember to factor in your travel time. To do a 45 minute sortie from Prestwick takes me at least 3 hours from my home in Glasgow once you include travel, getting the plane ready, taxiing, putting the plane away... Also at this time of the year, time is light limited (as you can only fly in day light during ab inito training).
I'd recommend that you find a school which matches what sort of pilot you are looking to become. Have a look around a number of establishments, have trial lessons at a few, then take your pick where you feel most comfortable, then search on here and ask about specific schools once you have done your research. Every school has its good and its bad points - nowhere is ever perfect (despite how hard people try!).
It is possible to do intensive courses to get your PPL quickly, but you will need to discuss this with individual schools. Like anywhere in the UK, training is weather limited. Some locations are more limited than others.
For example, Prestwick (where I am) is pretty much never foggy and normally has a fairly high cloud base so there is often an exercise of some sort that can be done - but I had lessons booked for nav exercises at various times over the Christmas break and I haven't got up at all. Flexibility is normally the best policy, so you may struggle if you aren't fairly flexible. Also, many people are brain dead after 2 intensive hour long sessions - there is no point wasting your money in the air if you aren't learning! In saying that - you are better to learn where you are going to do most of your flying, so missing out on a few lessons is a good lesson in itself about what you can and can't do with your licence once you have it.
The more intensive the course, and statistically, the younger you are, the quicker you will complete the training. 45 hours is a minimum, and possible, but very rare. If you have a long break between lessons you will back track and so will need to spend extra time re-learning. Many who plan to fly as a hobby are around retirement age and out of the pattern of learning new things and doing exams so it takes considerably longer to complete the course. You will move through the course on merit - not on number of hours - so its up to you to prepare to make the most out of the time. I haven't heard of an official average, but I'd say its around 55 hours.
Medical wise - it depends on which licence you go for. For an NPPL (I'll ignore the new EASA versions but they are expected to be equivalent) you need to get what an HGV driver would get from a GP (see
http://www.dft.gov.uk/dvla/medical/~..._a_glance.ashx. For a PPL a Class 2 medical
Initial JAR Class 2 (Private Pilot) Medical Examination | Medical | Safety Regulation or a CPL (for doing work as a pilot) a class 1 medical which is more stringent and involves a trip to Gatwick. If you are concerned, it might be worth doing the medical first to see whether it is a problem. I can recommend you a very friendly and relaxed GP in Cumbernauld who wasn't charging silly money who can do them (and he has a PPL and flys from Cumbernauld himself). He was even able to do it just after surgery hours for me so I could do it after work. Private message me if you want details (or search on the CAA website).
Weight isn't a problem for me so I can't comment on a maximum BMI that is acceptable. If you are as over weight (or just very large) as you suggest then it could effect what aircraft is suitable for training or which instructor you use as in many two seat planes, two large people plus full fuel isn't possible. You don't need me to say how much better you will feel anyway if you are able to keep your BMI sensible!
Lastly - if you are looking for a more student friendly forum - try the "Student Pilot" section of
FLYER Forums • Index page. In saying that, I have learnt alot by lurking here over the past few months, but you do need to be careful to separate out best practice from personal short cuts (and once you start your training - your instructor is always right...).
Good luck - and it is something definitely worth doing!