> My fat ass would have given up before I even reached the Bay Bridge

Cycling is a fairly low-impact activity for your body, and is a great way to get some exercise if you are out of shape, with a fairly low risk of getting exercise-related injuries. (Compared to, say, running)

The only thing you'll really need to "train" are your "sit-bones". A good, soft-ish, wide saddle will help, as well as padded shorts. In fact, for your comfort, padded shorts are a must-have.