I finally had a chance to look at seriously fish closely and compare temperature ranges. Here's what I found:
Pygmy Cories: 72-79° F.
Betta: 72-86° F. [I wouldn't keep them that high or low myself] Bristlenose Pleco: 69 - 79° F.
I think I'll get pygmy cories, then, once the tank is ready c:
So, how many? Does 10-12 sound good to everyone for my size tank and stocking? I plan on adding more mystery snails fyi