I agree with the others that you should keep on doing what you are doing for the moment. The problem with being in the so called "morbidly obese" category, is the worry that if you do too much before your body is ready for it, there can be health issues to worry about. Once your fitness and weight has improved by regular and longer riding, then you can think about full-on training. If you really want good advice, you can talk to a doctor or trainer about what is best for you. After all, everyone is different.

Keep at it though. It sounds like you are doing great.