First thing I would get a SW
(Salt Water) master test kit so you can check the ammonia/nitrite/nitrate levels.
I understand you have a tank with "equipment" but that really doesn't say much. Do you think you could give us a run down of tank size, if you have a sump/skimmer/powerheads. What is your setup what substrate do you have. Maybe a photo?
There are lots of options for you. It sounds like your rock will start the cycling for you. I would suggest that you post some pictures of the snails and worms for identification but since you don't plan on going reef it's not a big deal. Don't be surprised if all the life on your LR
Depending on the size of your tank there are plenty of fish that can go with shrimp and hermits.
The first two (Mandarins) are my favorites but require an established tank and are harder to care for the last one (firefish) can go in almost any tank... as long as you are not worried about the firefish getting eaten, also they tend to jump so you want to make sure you have some kind of screen or lid.