First off welcome!
Now to some clarity. One, betta do great in a heavily planted tank. For example here is my five gallon. Note the Betta lol.
Next up... No you should not do five cpd in a 2.5 gallon. Though CPDs are great for a five.
The think to remember when stocking a nano tank is to think of it like a doll house. Don't put big items in that take away from the tank.
What can go in a five? Many, many options. Many of which will start arguments on this site more than most.
Endlers (males preferably)
Betta (1m or 1-2 females)
Green Neon Tetra (not really green)
Celestial pearl danios
Many types of rasboras (some are incredible looking)
Some types of Killifish
Smallest two species of the shell dwelling cichlids (Lamprologus Ocellatus or neolamprologus multifasciatus/similis)
Smallest apistograma (its not colorful)
For breeding only or grow out many many more. However this list is not near complete.
Just go by max size when looking at them. You are building a doll house.
I wouldn't consider shrimp or snails against the bio load.
If multiple fish please use real plants and hiding places. Though you could end up like me and needing to do nitrate supplements. Who would have thought that? But I just had to order some nitrates for my tank.
Hope this helps!