It doesn't really matter. I'm sure there's an optimal spot if you measured all of the possible currents caused by the output that would bring the most dirt in contact with the input though.
I prefer to put it at the opposite end of the return. IMO this createsa current across the tank (return to intake). You'll notice at feeding time, as the food falls down from the surface, the current from the return drives food towards the end of the tank. With the intake at the end, it usually draws waste in as it travels towards the end of the tank. Just my observations and preferences though. Good luck!
I recently had 2 AC 70s on both my 40 breeder, and my 46 BF. I have since replaced one 70 on each tank with Emperor 400s. You can never have "too much" filtration. Possibly too much current, but not too much filtration.
Having more then one filter plays double duty. If for some reason one of the filters should go down for a short time the other filter will pick up the slack until the other one is up and running again. As a rule, there is no such thing as overkill or too much filteration. As long as there is not a tornado in the tank you are fine with all of that filteration.
Its not a stupid question at all! It was really puzzling to figure out where the best location is for the intake and return when I made the jump to a canister filter.