Congrats on finishing your first Olympic Distance. I only have a couple of these under my belt. I prefer a sprint+ distance, myself. The Half-Ironman is a large step up. I did what you are planning to do. Had a couple Olympics and then did a half-ironman. The big difference is food during the race and being ready to run that half-marathon. For me, personally, I hit a wall at the 5k mark into the half-marathon (please note, my strength IS the run). In an olympic race, 5k is the halfway point. In the half-ironman, the 5k means 10 miles left!
A little advice for the swim, I like to be on the outside of the swimming group and then swim straight to the buoy. It's a little longer, though arguably insignificantly longer especially when considering you will probably swim more consistently not inside a large pact of people. This will also help you from being mislead by errant swimmers who aren't going the most accurate direction.
Congrats again and step up that training if you really want that half-ironman.
