I arrogantly kept a white sturgeon in a warm community tank, and the heated water wasn't bad on him. The only problem was as soon as I went to sleep, I woke up with a dead sturgeon, and an angry 'gator gar.
As for the tank issue, you've really no need to worry, about keeping him in the 55g for a bit, these guys take years & years to mature. My LFS keeps 5-6 of them constantly in a 80g display tank with motoro stingrays, and they're happy as a clam.
On a related note; WOW. You guys pay that cheap?! I got ripped off! Mine was $79.00... For a 3"..