I have possible plantar fascias. Pain on foot, worst on arch. I already have flat feet. What is best treatment? What about shoes and pads?

See foot specialist. if your feet are truly flat, there is unlikely to be a best treatment. Treatment should be chosen based on your goals. An active person may not have enough control from shoes, pads, orthotics. However, a properly made orthotic can do wonders. There are also surgical options that a foot and ankle specialist can review with you. .