You can put anything into the tank until the tank has cycled. Using all cured live rock will make that happen faster though.
Corals (like all inverts) are generally not as hardy as fish, so I usually suggest waiting a couple of weeks past the first fish to add a few. Then, as long as you have the right lights, go ahead and add a few hardy corals.
For the first few corals, stick with the hardy stuff like soft corals and some LPS corals. SPS corals do best in tank that has had some time to mature and settle down.
I suggest adding a few snails at at time as you get more algae growing. You dont want to add so many snails at once that they end up starving.
Does that help?