ohms question

I am together a putting together a dedicated mono system in my basement, just for fun. Basically building it from stuff in the basement I already have, which includes an old onkyo tx 4500 mkii solid state stereo receiver that says 4 ohms on the back and a pair of 4 ohm speakers (some old Allisons). It would actually work best space wise for me to use one speaker.

Is there an issue in doing that? Or do I need to put a load on the other channel? Does it make a difference if I spin the balance knob all the way over?