Well first is to get in the pool. Don't worry about races. Open water swims would be great to eventually add on, but depending on where you choose your 70.3 (or whatever race) , the ocean is a different beast. So get comfortable being able to swim however far and then the rest is a on the day 'learning curve'. Granted swimming in a group can be crazy but I found no amount of pool/fresh water swimming prepared me for the salt especially, and waves. I've only done 2 sprints and I hated them. They are literally a flat out sprint, start to finish. And that's not my jam. My first tri was actually a 70.3. If you have the bike down, can get the run fitness back, and can just work on your swimming, then I say just go for the 70.3. Even though they can also be aggressively quick it's a very different race to the sprint. (to be honest this is why the full IM appealed to me - its not so frantic the whole time) Saying that though, if Trinity is across the road then it would be silly to not try them out. If for nothing else to test your kit and just have a go. But I still think you're safe picking the 70.3 as your main immediate goal.
