I kind of wing my peach pies as we pick our own peaches off our tree. I use my 10 inch Pyrex plates and enough peaches to fill them level. Our peaches are small and usually have guests (we don't use pesticides) so that can be anywhere from 10 to 15 good size peaches. The most important tip I can give you, however much sugar you put in your pies (I usually do 2/3 to 3/4 cup depending on how ripe the peaches are) mix into the sugar 3 tablespoons cornstarch and 3 tablespoons minit tapioca and then gently stir it into the peaches right before they go into your pie shell.
The cornstarch thickens the juices as the pie cooks and the minit tapioca continues to swell as the pie cools.