3-4 watts per gallon of pc, vho, mh, or t5 should be fine for Xenia. BTW, with anemonies, it's not the spectrum that causes one to need mh it's the intensity of the light. You can get NO output bulbs in the same spectrum as MH. It is also somewhat debatable as to whether you actually need MH, but it certainly makes it easier than PC or VHO. T5 may be usable too I think.
How big is your tank (gallons) and what are the dimensions?
Xenia will eat food given from the zooxanthelae (sp) living in it. It also gets nutrients from the water which I believe includes nitrates.
Your oscellaris may want to live in any coral really. Especially those with decent sized tentacles. Star polyps might work. Hammers, frogspawn, torch, long tentacle plate are some LPS corals that might work. Of course mine would pass up all of that in favor of the powerhead so you just never know.