I started riding about 2 months ago. I had the same idea. After a few rides, I just stopped caring what other riders thought, and just focused on the task at hand. I weighed 320-325 2 months ago (and could only do 3-4 miles at a time), and am now down to 285 and doing 30+ miles a day. If you're in it for fun, have fun. If people want to have fun by looking at you, let them have it. You'll feel better once the ride is over, and the results will start to show quickly. I'm still figuring out my gearing, it takes time. It's a fun way to get your exercise, and fresh air. And you'd be surprised what bikes can handle for weight. I went from a trek mountain bike, to a road bike quickly, and nothing is the least bit shaky about it.