not all two Fh are alike.. not all Fh are aggressive.. some strains are more aggressive than others.. basically all FH got their own characteristics.. some are docile while others are glass bangers..
also depends how they are raise, what type of setting.. water warm or cool.. how big the space and how often fed..and even the type of food and the amount will also changes the differences of their aggressiveness.
typically the bigger the room the better for FH.. but if any a 40 gallon tall would be suffice for an adult Fh.
and yes the more info the better when raising a PET