I would say that your tank should be no smaller than 75 gallons. This fish will get about 12" when full grown and likes it's water warm (80-90F). A fish of this size is happier when the tank is more than 18" deep and at least 4' long.
As far as the husbandry of this fish... It depends on the size of your tank. If you have a 320gal tank, you could keep it with a slew of other fish. However, if you're going to keep it in a 4' tank, I have a feeling you're going to end up in a species only tank. You MAY be able to keep your flowerhorn with another particularly nasty American Cichlid that gets about 12" like a Festae or Trimac. If they grow up together, you'll be able to gauge. You could try a breeding pair, but don't be suprised if one ends up killing the other.
My recommendations is that if you want a breeding pair, get six babies, let them grown and when they start to pair off around 4" select the pair and sell the rest back to the pet store. I'd throw some dither fish in there too like a large school or Giant Danios or Columbian Tetras or Serpae Tetras or something. They might end up disappearing eventually, but they'll divert the agression sometimes from the other cichlids.
If you wanna try with other cichlids, then buy your flower horn baby and figure out what other cichlids you'd want to try with him. If the cichlid is less agressive than the Flowerhorn, the general rule is to make the more aggressive fish the smaller fish so he's forced into a submissive position from the get-go and he can grow out of it. Try Texas (Cyanogotus, not Carpintis), Festae, Trimac, Managuensis (Jaguar), Red Devil... I'd stay away from Green Terrors, Jack Dempseys or Oscars since they're big but not quite as aggerssive.