As for food, you anemone will feed on the frozen meaty foods that you feed your fish.
as for adding any suppliments such as calcium, buffers and trace metals.. You should ever add anything that youre not testing for. Especially things like iodine. Iodine can be toxic at levels that are above natural sea water.Iodine is quickly converted to iodide in our tanks so it can be difficult to test for. When it comes to iodine, there is plenty in the salts if your doing water changes. Many foods are high in iodine..
Many people beleive that the only suppliments needed (if your doing waterchanges) are calcium, alk, and sometimes Magnesium. but you should be testing for these. If you dont have a lot of stony corals, you will likely not need to suppliment these either if your doing water changes with a good salt. Again, you dont want to blindly add CA, ALK.. adding too much of one can drive the other down.