Husband has marble size gallstone. Has had some pain, but not severe. Should surgery be performed immediately? We are waiting on our insurance.

Wait. I would recommend avoiding fatty foods and waiting for your insurance to kick in. If he has severe pain or vomiting or fever or jaundice you should take him to the emergency room.
Elective surgery. Ideal thing is cholecystectomy , if is occasional mild pain , he can plan surgery when gets his health insurance, be aware some insurances do not cover for preexistent diseases.