V. My first Tri was Oly distance: 1.5 km swim, 40 km bike and 10 km run. Total time for you would be between 2:30 and 3 hours based on your fitness. It might be the right place for you to start. Oly distance is interesting, it's not a sprint effort but it's pretty bloody close. Kinda like running the 800 in track.

You can really handle the bike and swim, I think that a sprint distance would not challenge you quite enough (based on your double century past). I think that 13 miles running is likely a little excessive for a starting point, although you might be able to go up to that distance fairly quickly. Yup, I'd say that Oly is the way to go. IMHO.