Pests

I just discovered in the last two days that have Aiptasia and Asterina star fish. I've had Aiptasia before, in which I used Aipstasia X to kill because my tank was cycling and I couldn't add a peppermint shrimp at that time. My hope was to add My first coral this weekend. So, my question is....is it OK to introduce a Harlequin shrimp and a peppermint shrimp at the same time and will they live happily in a 20 gallon tank without eating a coral? If not, which one of these pests should I deal with first? I feel I have way too many small Aipstasia to kill them all using Aipstasia X. I'm certain there are more in there that I'm not seeing. I can barely notice some of these, as they're so small. The star fish, I'm only seeing about 5 or 6 of them at the moment.