Recovery time is somewhat unique to the individual. I just started tris last year. Did a HIM in May and did very little for at least a week. Did my second HIM in September and was running again in 3 days without issue. I suppose it also depends on how hard you go, too. Lots of variables.
If your HIMs go well, there's no reason to believe you couldn't be ready for a full next year. I'm not a pro, so take the advice with a grain of salt
Yes, you can do both races in a year. I plan on doing the same thing in 2013. Generally, you should give your body 1 day of rest for every hour you spend racing. There are other factors that come into recovery time like how hard you race and your fitness level. During your recovery time, good massages, stretching, and super easy paced recovery workouts will aid in your recovery as well.
I finished my first HM last weekend and set a PR for myself and it took 2 days for me to recover. Tights, stretching, and massages helped lots! Still had some sore spots day 3 after the race and ran a short 30 minute recovery run day 4. Legs were 100% back that day and felt good. =)
I plan on doing the same thing, probably the same races you are speaking of.
Galveston in April, Austin in Oct. and Woodlands 2013??
You could play it safe. Hold off on registering for the October race, until you complete
the first HIM, and see how your recovery goes after that race. I'd guess you will be just
fine doing all 3.