I'm new to this but I have a 40 gal w 5 fish, shrooms, & suncoral
42 lbs LR
I have:
1 fighting conch *very cute* wish I got 2 but only 1 to a 30 gal tank- sifts through sand
1 emerald
11 scarlets (bcus blue legs may kill conch for shell)
8 turbos
2 peppemints (to kill off aptasia anenomes)
1 cleaner
1 brown brittle star
up until 3 weeks ago I had 2 snails & 2 scarlets I felt there wasnt enough in the tank for them to eat & I did lose 2 sails I fear it was due to starvation bcus when my 2 snails that I still have look like the other 2 did the day before they died I feed them a piece of an algae sheet & they look fine the next day. I do the same for the crabs I put a piece of an algae sheet under a rock so they can eat it. about the size of a business card.
I would start with a few since you dont have much in your tank & add on as you need more.
I would say 5-6 turbos, 10 nassarius snails, 1 conch, 1 cleaner shrimp. That should kick just about everything in the butt. I'm not a big fan of crabs as they can get offensive towards corals. The nass snails will sift sand for you.