Wow- congrats on a great 5K run!!! I'll bet you feel so empowered now that your running has returned. So many options now.
Go for the Irongirl next year. I had some friends do the one in Dallas, and they said it was the most fun they've ever had at a tri. By then you'll have plenty of time to get swimming down-pat, and work some more on your running. How fun!!

and about the walking in the water: my IM in 2 weeks is in a lake that (because the city forgot to put in a request for more water) is pretty low. I'm hoping that on lap 2 I'll just start some water running if I get tired. Nothing wrong with that! It's kind of a triathlon/duathlon combo that way.