Sounds like a great stock to me!
you could definitely add a few more pandas (and even a couple more neons) though- they're adorable little guys, you'll fall in love and probably want more anyway
I find they're more active in a larger group also.
If you can, try to get a beta that is kept in a tank with fish. I have seen some LFS do this and it's a great way to ensure that the beta will get along with other fish. If you can't find any that aren't in cups though I still doubt you will have problems with corys or neons. Betas mostly only have issues with other long finned fish.
Good luck!
Oh by the way, make sure your tank has a sand substrate for the corys. They like to filter the sand in their mouth and out their gills to eat any food particles. They're so fun to watch