Corys sure, betta no...unless you like the torn fin look. Not to mention D. margritus are very active and might stress him out. And if not he might stress everyone else out...by murdering them all one by one.
I think you should leave the Siamese Fighting Fish out but that’s just me . I do love that you used that very old term rather than BettaSo now I've changed my Oase 100 filter to a 200 which filters 650 litres per hour, I have found that I can add a few more fish.
So as well as the Microdevario kubotai, Boraras brigattae and Danio margritus, I am thinking of adding 3 or 4 corydoras and possibly a siamese fighting male as the centerpiece. What do people think please?