Sorority Companions

Okay so I have a 15 gallon sorority with 5 girls atm, along with 5-6 ghost shrimp. The substrate now is sand, but I am switching to gravel next week. This gives me the chance to get more fish! I am changing the layout also.

I was thinking of getting any one of these, not all:

1 or 2 more girls
school of cherry barbs
school of neon tetras
endlers, if I can find them locally

My pH is around 7.8-8 and I forgot how hard my water was, it is on the harder side.

Any other ideas are gladly welcomed!