Update: A great local freshwater specialty store got a shipment of pygmy cories in early, and I picked up a small school of 6 on Friday.
They are doing excellent so far. Most went right to work in vacuum mode within a minute of releasing them into the tank, and my Betta hasn't been aggressive at all, other than a short chase through the tank with one pygmy when they were first introduced. After learning how quick they are, he pretty much ignores them and shows no signs of stress.
Really cool little fish. Very lively, active and playful. The owner of the LFS said I could put more in easily with my tank setup, but I'd rather them have more space and filtration than they need than not enough.
I also picked up a black mystery snail a couple weeks ago, which I plan on moving to another tank soon. Betta was curious and nipped at it a couple of times after first introduction. I was ready to remove and return the snail but he got over it quickly. Now he does nothing more than play with her algae discs from time to time
Water parameters are great and I've had no issues so far. Thanks for the tips everyone :)