Hey-you have already identified one of the most major items..........that is having the desire to improve. You also have the experience on knowing what it felt like to ride faster and longer so you have that going with you as well.

Now it's just a matter of having a plan. I'm thinking the plan should include getting your weight down considerably. That can be done with a combination of increasing your exercise (more time in the saddle) in conjunction with reducing your overall caloric intake. As others have mentioned, you need to document what you're doing. You need to have a tool (whether electronic or manual) to document both categories.

I think the on bike performance improvements and confidence will come as you concentrate on the riding time.

If it helps any, I went from 225 lbs to 165 lbs over about 18 months and was able to aaccomplish what you're wanting to do so it is very "doable". Go for it and keep us posted on how your doing. As you know you'll take several steps forward but probably also will back track a little. It's just a part of the routine.