I'm doing my training in Inverness, and enjoying the flying a lot. I have to go back to finish a few hours, but the weather was fairly good and I think that during the month I was there we only missed one whole day and a few mornings due to fog. Landing fees are included, so it works out relatively cheap too. If you're considering an intensive course, it may well pay to look further afield - if it costs 40-50p/mile then a b&b at £20 a night works out cheaper fairly quickly.
If I were you I'd join
AirQuiz - Online Practice Examinations for Pilots! or similar and buy a course of training manuals before starting. Even though I'm reasonably bright, I found that there was quite a lot of material to get through, and I don't think I could have done an intensive course without having gotten most of the theory out of the way first. Also, get your medical done before starting anything - particularly if you are worried about your weight.
BMI is (weight in kg)) / (height in metres squared) so you can work out your number. If it's under 30 (and possibly rather more) you shouldn't have any trouble. At your age, you would have to be unlucky for your weight to be causing any medical issues that would stop you from flying (e.g. heart disease) but obviously keeping trim will be good for your long term health and I wish you luck with your fitness programme.
Have fun.