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?
It won't hurt with solid state but would sound better with two. It could still be made to be mono.
Do what you want with that gear. Its 4 Ohms for both channels fret not.