Have you taken a look at other species that are better suited or are you really set on a Flame? I really like a few of the dwarf angels too, but I like my corals (and clam!) better. I also think your tank is a bit small for a Flame. I wouldn't put one in a tank smaller than about 30 gallons, and i think yours is 20 if I remember correctly?
Check out this website for other ideas:
http://www.nano-reef.com/fish/
Personally, I think your tank would be perfectly suited to a Jawfish, and then maybe an Orchid Dottyback. Or a shrimp/goby pair instead of the Jawfish...?