Just a heads up, I traded my 14" Asian RTC (too mean) to a guy for a 2-3" SA RTC about two weeks ago. He's already grown about an inch.
They grow very quickly, and when they get big, the cost of feeding goes up. I'm working on a pond for mine too. His quick growth in the past couple of weeks already has me scared that I might not be digging quickly enough.
I got my TSN in August at around 10" and he's already closing in on my 20" black aro. He seems fairly content in my 450g at the moment, but if my pond isn't finished by spring, I'm going to have two very unhappy fishies.
Also, don't forget about all the little expenses that go along with a pond. A heater, a pump, a liner, etc all add up in price quickly. I spent more on all the little things for my 450g tank than i spent on the tank itself.
Not trying to be rude, just trying to give you a heads up of whats required for these fish. The fish will love you more if they're treated properly.