Hi ccbram,
I did the same thing and purchased a MI from LiveAquaria (I had just missed the DD one too, those go ridiculously fast). After drip acclimation I put her in my 150g reef tank. While seemingly healthy she was still slightly thin as I could see her spine somewhat. At first she was picky and did not eat much the first week. So, then I started to feed her different foods daily hoping to get her to eat well.
Later the first week I gave her New Life Spectrum Marine Fish Food pellets twice a day plus varying frozen food once a day (PE Mysis, Hikari Angel, SFB Plankton, ON Chopped clams, F1, F2, Prime Reef, and Special Formula VHP ). She seems to like the Hikari Angel a lot and I have since stopped the ON except for the Chopped Clams.
After the first week she was now eating the pellets pretty well but still showed her dorsal bones so the pellet feedings were increased to 4x per day plus the frozen 1x. Amazingly, after two weeks her body had filled and no longer showed any of the bones one her sides. Unfortunately, I was about to travel so for the next 2 weeks I had her only on NLS pellets 5x per day.
So, about a month after getting her I dropped the feedings back down to 2x NLS (now using Thera-A which she seemed to prefer over the regular Marine variety) due to higher levels of Phosphate and Nitrate. At this time she also started eating nori. So, once a day or more on weekends I give her a quarter sheet with some Selcon soaked in it (most of the nori is eaten by my Blue tang even though he gets his own clip).
I will also sometimes give an extra feeding of Marine S. I've had her for about ten weeks now so far so good...knock on wood. She is by far my favorite fish.
I got my first Moorish Idol a few years ago (my wife had bought her for me, yes she's a keeper) and kept her for about a year and a half before she died during an overnight pump failure (lesson learned, now have the Ecotech backup battery).
Good luck with yours.