All your planned fish species aside from Parosphromenus like harder water
? These fish all share their habitat with paros en Betta, except for the shrimp. These come from swiftly flowing streams, thus making a strange combination with the fish. Wouldn’t do that myself.
I agree with Sverting. Paros can live in tap water and even prove quite hardy. The only thing is they’ll never colour up like they would in acidic water, plus they won’t breed.
KH is a pH buffer. With a measurable KH, pH will never get low. This is the reason KH is always 0 in acidic tanks, whether pH is 3 or 5. I don’t think KH is of much relevance besides keeping pH up. There must be some other factors, maybe including luck.