You don't necessarily have to limit yourself to just a few fish. You have to be reasonable in your selection though. Having multiple fish that can get up to 10-12" in a 55 gallon tank actually limits the different kind of fish that you can keep MORE than sticking to fish appropriate for your tank size does.
I'm not saying that there is necessarily anything wrong with your approach to fish keeping. But I wouldn't be able to do it. I couldn't bring myself to buy a fish knowing that I was just going to return it once it got too big for my tank. One, I would become too attached to the fish after watching it mature and grow. And two, I would be worried about the fish's future after I returned it. I mean, there aren't many people that want to buy a matured fish. So more than likely it will spend the rest of its life in a small LFS tank or worse.
But hey, that's your prerogative, I'm just stating my point of view
