On a 55 gal
tank 4x65w PC
or 4x75w VHO
would be just fine. I would not really suggest the MH
if the BTA is your primary goal. It may well end up adapting to the MH
intensity over time but I do not think it will flourish as much.
You will still be able to have many coral in the tank as well if that's a concern. As far as the anemone moving about, your just going to have to let it be. It will eventually stop once it's found the right flow and intensity that suits it's needs. Unless the BTA is in danger of an intake device, it should be left alone. The clown will adapt.