I've been trying to research this fish a lot because I definitely want one or three. One interesting and important thing to think about is breeding. The cacatoides is a harem breeder. You'll want either a single male (that picture really is garish) or one male and several females. Getting it either way will be difficult. The males are very vibrant and colorful while the females a basically yellow so people sell them in sets to assure that they all sell. I'm sure that you can find someone who will sell them singularly, especially if you want several females.
If you do decide that you want to breed then you'll need a decent sized tank but these fish particularly seem to love an intracate setting full of plants, wood, and caves. They are small fish with small teritories but they will probably want (3 foot radius) more then you can get away with (10-15 gallons per fish) in a well arranged tank. A 29 gallon tank should be able to maintain two females and one male. They are very good mothers (I've heard) and some people even suggest that the fry can be raised in the community tank. You will need a fry basket however as after mating the females will not tolerate the male until the clutch has hatched and the fry are raised.
I'm considering possibly one lone male (large territory/20G) or two females and one male (tight squeeze/7G per fish) in a community tank.