There's another forum I recently joined (I can PM you the name if you want, not sure if it's associated with this forum so I won't publicly post the name) that has great-looking tanks.
If you go big, go big or go home. I'd do a low-tech 29G (similar dimensions to a 20G Long but taller). That way you can get some Corydora for the botto/mid-level, shoaling fish for the middle, and a Betta for the centerpiece. You could keep all 3 snails in that tank and keep the 3.7 as a QT for new friends or as a hospital tank.
Lucifer, Gabriel, Titan, King, Finnegan, Fin-again & Ricky.
Lucifer & Gabriel are my only non-rescues...