Still in the beginning

I started a 5 gallon tank last month. I went to the LPS to check my water. He said I was ready to buy a fish. He said 2 weeks after, come back and check the water to see if my water is good for more stuff. He told me a list of fish to buy and I decided on a Bangaii cardinalfish. I also have a hermit crab that I was told to buy while cycling. I later found out the crab wasn't necessary.

I am wondering if I am ready for coral. Do I have the right fish? Also, please keep in mind that everything must be seahorse friendly.