parrots aggressiveness varies alot. the upside is a bp can't close it's mouth so it can't do much damage. they get about 8 inches long (with the fins) and are very hardy fish. ph doesn't matter much as long as there are no big swings in ph. they can adapt to whatever your tank ph is. temp is the same as any tropical fish. they also eat anything so there isn't even any special requirement for food. they can eat pellets, krill,bloodworms, etc. anything that they can get in their mouths. they are pigs and will eat constantly if you let them. and they beg.
I have 3 very large parrots in my 140. The tank mates have excepted them. Only down side to them is they can't defend themselves against aggressive tank mates. Good luck to you and your new addition!
I have one.....Fred, SHE is around 9inch now huge fish! about 3inch thick. She does want to fight sometimes with my severum but that only lasts a day then they are best of friends. I've had her 3 years from 3.5inch to 9inch ( yeah yeah i'm just an excellent fish keeper )
I change the water every 3 days 50% its 100Gallon with 9 fish, i have to get sinking pellets so she gets to eat, floating pellets she has trouble with.
I feed live brine shrimp once a week, if your going to house it with other fish then make sure you buy enough so it gets a fair chance of eating.