My lfs charge £21.50 for 3 Pandas lolI would start by filling out the panda cories to a total of 6. Then maybe a small group of rasboras or black neons.
Don't put a male betta in with those fish. Bettas are known for not getting on with gouramis, and danios and tetras are extremely likely to nip the bettas fins. If you want a betta then get him a separate tank.