The least killis were okay with adult shrimps. However, I have seen large females take a swipe at baby shrimp. they also sort of roam the plants so I'm always worried about them looking for baby shrimps. I highly recommend the chili rasboras. they are more colorful and once comfortable they are out and about more. I haven't seen one go after baby shrimps yet.
As for the fissidens, I haven't done anything special. For some reason they grow better in this tank then in my "high tech" tank. Maybe it is the aquasoil/lower overall ph? i'm not sure.