Don't rely on the cycling to solve the weight problem. It'll help - it's possible that it will help a lot - but controlling what you consume is the crucial element.

You can accomplish a great deal in a year as far as your fitness is concerned. Your first priority should be to build a big base of aerobic fitness. Once you have done that, you'll be better able to tolerate and benefit from more intense training. Building base is a matter of putting in a good number of hours in the saddle at moderate intensity. How many hours a week can you devote to cycling?