Have overpronation & bunions, how hi can shoe heels be w/o problem? sneakers seem to be on a platform how hi can they be?

The less the better: Any high heel will aggravate a forefoot problem like bunions. So the smaller the heel, the less the load on your forefoot. If you have to wear one, wear one with a bigger toe box, and width enough to accomodate your big toe joint.

High heels & bunions: I would recommend you not wear heels over 2 inches and even then, depending on how rounded or pointed the toes are, shoes can aggravate and make worse a bunion. If you are overpronated a heel of around 1 inch is good. You also need to go by your symptoms. If shoes hurt, do not wear. Get evaluated by a podiatrist is best advice. They make dress shoe orthotics which may help the pronation issue.