Yes other shrimp can be kept with a pistol.
Tail Spot would be fine.
CUC can be made up of almost any scavenger. Mainly snails, others will recommend hermit crabs but not me-lol. If you do get one, get only 1.
Porcelain crabs are cool but very elusive filter feeders.
As for a Star Fish. Your tank is to young and small for most. Only one I can think of doing well would be the Brittle Star.
Good luck and keep us posted. Remember to ask here first before you buy...could save you lots of $$ and heart ache



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