I've been there before...
which reminds me they had some awesome deals on coral when I was last in there; I should go again.
I think I'd personally keep the tank, and run 2 filters on the 55 at first, to keep 1 seeded and available to switch to another tank.
keeping endlers in a 37 will result in a large number if you have a mix of gender.. but you likely know that. having somewhere to sell or gift fry or juvies will prevent a need for a bigger tank.
A QT tank is always a good idea, but I get the feeling you'll set it up as a regular tank without much time passing