RE: 22 stone and Want to do Weights!
just my opinion
1 - training with weights will increase your muscle mass, this increased muscle mass will allow you to burn more calories due to your metabolic rate increases, therefore complementing your overall goal of lossing weight.
2 - X
3 - An average male needs 2500 calories a day to maintain a steady weight, to loose weight you are required to eat below your levels of 3900, however by drastically cutting your calorie intake from 3900 to 1500 would be hard for you to achieve. I would advise steadily dropping this level as a sudden decrease will mean it will be hard for you to be able to sustain a decent amount of muscle mass
4 - its best to ask this question in the diest and nutrition section as there are a variety of different variables that need to be taken into consideration before a good estimate can be made
5 - running, swimming etc... will not hinder you goals of building muscle if completed in a complementary way with your weight training, e.g on seperate days. Also for someone your size i would not suggest running as your main source of cardio i can speak from experirence it will not do your knees and jionts any good and could give you shin splints. Instead i would advise something that is lower impact such as swimming or cycling.
hope this helps