I can't offer any advice, I'm afraid, but I do want to wish you the best of luck with your venture. As you say, you'll probably want to get yourself something with wide tyres, and probably without rear suspension. Don't forget, too, to concentrate on eating well. My personal advice would be to cut out all sources of carbohydrates and refined sugars but to worry less about eating healthy fats and get plenty of vegetables. And, much as I love cycling, don't underestimate the health benefits of walking, too.
John