Add as many sexy shrimp as you want (5 or 6 make a nice group) they add very little to the bioload and get along with everyone.
Bumblebee shrimp are also tiny, but hide too much, are delicate, and I've had one kill a second one I tried to add to a tank. Never had one last more than 6 months and rarely saw them.
I'd be careful about another pistol shrimp since I don't know if there may be compatibility issues with the first one.
A cleaner and a peppermint should be no problem.
Give away a few hermits. You'll have enough scavengers without them.
As to other shrimp, go on Drs. Foster and Smith, look under invertebrates and in the Divers Den section. Any anemone shrimp or similar will be fine.
http://www.LiveAquaria.com/product/prod_display.cfm?c=497+525+700&pcatid=700
They do not need a host anemone to survive.
Tozeuma Ghost Pipe Shrimp (Leander plumosus) are interesting, easy and safe.
http://www.LiveAquaria.com/product/prod_display.cfm?c=497+525+1970&pcatid=1970
Banded Coral Shrimp with the blue thorax, (Stenopus tenuirostris) stays small and is not agressive. My pair is with me over 2 years without a problem.
http://www.LiveAquaria.com/product/prod_display.cfm?c=497+525+1134&pcatid=1134
I would NOT try any other Stenopus in your tank.