Well, if you can afford a 12'x24' and have the space for it, then by all means go ahead.
If you don't even have the space to start off with, why would you keep a gator when you can have all the other species?
And even if you have a 12' x 24', the next question will be if one wants to maintain it as a species only tank? Given the fact that gators do not com well with most other fishes.
In addition, 10" for a 6 month old gator? Seriously, is it really growing at the rate it should be?
90 gallons? So is there a plan install when it out grows the 90G?
All I'm saying is that one should not even start what he can't finish.
Sorry, didn't see that you have a 3' pond on the way. Anyway, 3' is not enough. And how many people have a pond in place?