Almost any extra info about yourself can help us help you.
I have some experience in your situation. I was morbidly obese at one point, weighing in at over 300lb. I lost the weight first, then built myself back up over a number of years. Yes, you should start lifting immediately. Lifting makes everything work better, wether your goal is fat loss, muscle gain, or some combination thereof. I went from 300+ down to just over 200lb in 1 year. Since then I've built myself back up to 235lb, with a very muscular build. I'm also much stronger now at 30 years old and 235lb than I was in high school at 275lb.
Current PRs at 242- 495, 335, 585, 1415