I've only ever done Ironman Canada so I can't comment much on the US races. On the Ironman website, you can pull up course maps with elevation profiles for the bike and run. Do this for each race you are considering and try to find the flatter ones. Florida is very flat, that's why it's a good 1st timer. I would expect that the newer IM additions would be easier to get in to but I'm not sure. As for the volunteering question, I have no idea.

Good luck and let us know how it goes.