I had a 300 van that used a quart or two of coolant every summer. I never found any place it leaked. I assume it was going out the tail pipe. I drove it like that for years with no ill effects and no noticeable loss in performance. It was a mystery that I never chose to investigate (removing a head or engine from a van is no easy task) but I suspect a flaw in the head gasket or sloppy gasket installation. It never got worse.
Your plan to drive and monitor seems right to me.
