Question #1: Yes, pond liners will entirely eliminate seepage. If your rainfall exceeds your evaporation your pond will stay full, and actually need a small emergency spillway.

Question #2: I would think that you could research other nearby ponds in similar soils. Sounds leaky to me. I like my liners and have found that you will actually grow rooted vegetation in the silt that finds it's way into the pond. The water actually becomes clearer over time because the macrophytes tie up nutrients, that are then unavailable for single-celled algae.

Question #3: If you don't trench tuck the edge, what will you do with it? It is unsightly if you don't hide it. Hopefully you will do a better job than me.

Question #4: I don't have experience with PVC liners. You would have to find someone who has one and do a cost analysis which would involve depreciation of the EPDM and the cost of replacement of the PVC when it wears out. You probably won't wear out the EPDM in your lifetime. I drive my John Deere Gator on mine without any concerns. You can't kill it. If there's a nuclear holocaust all we'll have left is rats, cockroaches, the Hostess pies you buy at the gas station and EPDM liners.

Holding a redear sunfish is like running with scissors.