The weight of the tank is distributed onto the stand, whatever type you purchase or build.
The wall doesnt make a difference unless you are putting it in the main level of the home, so we need to know where you are planning on putting the tank?
Main floor (entery level) then yes you need to support the floor, In a 55 I really dont think it will make much of a difference as long it is near a load bearing wall, I have heard of 55's bowing floor's in apartments.
Now my 210 is in the basement, if I wanted to install the 210 on my main level of my home I would have to support the floor joists, you can purchase supports at home depot if you really need them.
If you have a basement that's ideal for a tank, no windows to worry about.
Not sure what you plan on doing with the 55 but I could easily see a 55 weighing 500+ lbs once full of rock, sand, etc.