Unless the dragonet is tank-bred, it may be difficult to feed. Sometimes tank "raised" are trained to eat frozen brine and/or mysis and pellets and or flakes, but it's not guaranteed (check with seller, or if possible, see them eating). If the dragonet is wild caught, it will only eat live food. Dragonets are NOT recommended for beginners or tanks less than a year old. Lots of mature live rock (1 pound per gallon minimum) is necessary to provide sufficient places for amphipods and copepods to breed, and a refugium is very highly recommended. I have both, and after spending hundreds of $$$ on pods, I have a good population after nearly a year. I planned ahead, seeded the refugium and tank for several months before purchasing my mandarin and scooter dragonet. Too many people rush to buy these fish, not realizing that they are condemning these fish to death from starvation. Do your homework and prepare well ahead of time.
Jay is correct. I have two firefish and two sixlines, and they get along fine. Get the firefish first so they can settle in... if you haven't already gotten the sixline.