I purchased a pair from LiveAquaria Divers Den. The female passed away while in quarantine. The male is a fantastic little fish. Yes, they do like to hide and will hide in the weirdest spots. I do have to spot feed him as they do not like to venture out (not to mention mine is in a corner right now). He likes big chunky foods, I feed him mysis and sometimes larger things if I have them on hand. I have no problems whatsoever with other fish and inverts as far as I know. Sometimes these fish can bother corals if they make their home in a coral, but otherwise completely coral safe. They stay small, only ~1-1.5". I seriously love my little guy, sometimes he is a pain when he makes his home in awkward places for me to feed him (and he will get the message by going hungry for a day or two). So overall the only special care is spot feeding.
Since you seem to be shying away from the croucher, which I can understand, they are not for everyone, I think a chalk basslet might be nice.
Saltwater Aquarium Fish for Marine Aquariums: Chalk Bass
And there is lots of nano fish here-
Nano Fish
Good luck in your search! Crouchers are not big yet in the hobby, so let me know if you need anymore help with them =)