I'd start with a mixture of sand burrowing snails like Nassarius and Cerith and more traditional snails like Astrea, Turbo, or Nerite. When I started, I had 6 Nassarius, 6 Nerite, 2 Astrea, and 6 Scarlet Hermit crabs. Hermit crabs are fun to watch for most, but there are differing opinions on how valuable they are as CUC members. Personally, I like them for entertainment value, but would stick with less aggressive ones like scarlets.
Stay away from carnivorous snails like bumble-bee snails and some conches. Blue leg hermits can be more aggressive and may want to try on snail shells while shopping for new homes (after killing the current inhabitant of course).
I'd add other members as needed over time. For example, peppermint shrimp for aiptasia problems or emerald crabs for bubble algae.