I assume you are referring to a haddoni? As stated, they will eat fish. I had to move mine to their own tank as I liked my fish.

I currently have two haddonis with 4 saddleback clowns. So far so good after 6 months or so. I do recommend sand as it is their natural habitat. 4-6" is ideal. I think mine have only 3 currently. Plan to add a bit in at least one area of the tank.
Saddlebacks can be hard on the nems. I think that is part of why I lost one. I would recommend clarkiis or pink skunks instead. FYI
You may need to treat the nem, so make sure to read the posts on anemone treatments. Very good to have on hand.
https://www.reef2reef.com/threads/protocol-for-using-antibiotics-to-treat-infected-anemones.758495/