Apistos, tweak the water with RO from the LFS, its only 60 litres you can keep whatever you want
Betta cocciana looks awesome, wish they had those for sale here... I only see crowntails, halfmoons and veiltails on sale. -.-There are several betta species that do well in pairs or groups, Betta cocciana comes to mind. Perhaps you should look at Dario dario, related to Badis badis but much more colorful.
Beautiful setup by the way.