We put metal valve stems on our tires when replacing them. Feel much more comfortable with metal. The stems on all our tires face the same way so that if needed we can use any tire in any location.
We use rib tires on the front and do not rotate tires. Did have a problem when running all season tires on the front. At about 15K started getting a vibration in the steering. Found it was caused by cupping/saw tooth wear on the front tires. So far have not had that problem with ribbed tires on the front.