You don't need any crabs and snails in this tank if you don't want them. They really don't clean up anything and you will have to provide food for them. If there is no food in the tank they will starve to death. Hermit crabs kill snails out of instinct.
If you like crabs and snails, get a couple/few of them, and not the ridiculous amounts they recommend.
As for the order of things, I would add fish, one at a time. After the addition of a new fish, the bacteria colony will have to grow to accommodate. Corals can be added at any time after the cycle IMO