I'm new and would like some help

So first off I have not set up a tank yet and I'm planning for one in the near future maybe next few months and I'm thinking about getting a 55-75 gallon tank or maybe smaller depending I don't know that's why I'm making a post but I'm thinking about a solo fish for an aquarium and would like to know some recommendations so far the ones I'm thinking of (not all three at a time of course) are an Oscar, red devil, and flowerhorn but would like to know more options that might be easy to take care of an preferably would like to know some non-cichlid unique looking ones preferably that need no bigger than a 75 gallon tank.