An extra 20 lbs on the front and back with the counterweight isnt going to break a 40 breeder ever, let alone in the small amount of time in an apartment. But yes, ideally they need plywood under the tank as I said. Im very familiar with 40 breeder tanks.

You dont really need anything to support the small amount that hangs over for that small a tank. If it were bigger i would have concern about stress points since tanks are designed to sit flush on each side. I had a few 40 breeder tanks in my day. Yeah its a lot of weight when filled, but the majority of your tank is supported. Ideally you want a piece of plywood under the tank to spread out the weight evenly. I have full support under mine and a layer of insulation foam between the wood and the tank, which further dampens any high points.