What kind of lights do you have? If you have lights that are suitable for a reef tank, then zoanthids, mushrooms and leathers would be great choices. There are a lot of different types of soft corals, but you can't go wrong with any of those three.
I would suggest you pass on anemones for now. They are very difficult animals to keep -- more difficult than most corals. They require perfect water conditions and very bright light. You have lights that are good enough to keep anemones, but they usually do not live long in tanks that have been running for less than a year.
You can, however, add corals to new tank, and a tank without fish. Some easy corals would be a good way for you to get started.
What kind of lights do you have? If you have lights that are suitable for a reef tank, then zoanthids, mushrooms and leathers would be great choices. There are a lot of different types of soft corals, but you can't go wrong with any of those three.