I may be getting a 55 gallon aquarium need advice!?

yes that is a good deal and frontosas are an agresive fish so any agresive fish you can put in that tank but dont use chemicals in your tank it shortens the life of your fish go get some fresh water salt when you fill the tank yous 1 tea spoon to every 10 us gallons the salt also will help if your fish get cuts or stuff like that i have a 90 gallon with a variaty of fish from sharks to electric yellows and other tropical fresh water fish i used chemicales when i first got my tank fish were dieing left and right so i went to fresh water salt havent had a fish die in 4 years