Purple Rose Queen Cichlids 6-8 inch
Rose Queens are essentially just a specific variety of Flowerhorn and should be cared for the same way.
For an adult Rose Queen, I wouldn't recommend a tank smaller than a 75 gallon aquarium. Full grown, they will likely be more than 12" in length, so you really want something larger than a 55 (which is only 12" front to back). If you want to keep more than one fish, I'd recommend going even larger.
In terms of water quality, they'll be just like any other South American cichlid. Relatively neutral pH (aka around 7.0) and relatively warm water (upper 70's). Large fish produce a lot of waste, so ensure you have strong filtration. For food, I always recommend a high quality cichlid pellet, possibly supplemented with frozen foods. This will give the best nutrition and avoid potential problems that come from feeding live foods, which typically are not the best choice.