I've tried a lot of floating plants myself before, but they all end up taking over the top if you treat them well. My bottom plants always ended up suffering.
From my experience, fancy male bettas will only pick on fish with large finnage like guppies. Otherwise they're too slow for most other fish when in a community setting. Also, they can become victims of fin nippers since their fins are so large.
I had goldfish (comets) and kois in the same pond before and I thought that was a huge mistake. Once the comets are the appropriate size to breed, they breed like crazy. Every spring, my pond would turn a dark brown color because of their breeding. If you want to enjoy your kois, I wouldn't...