Did you look at the Cambria edge profiles? They are available in different thicknesses. Another alternative would be to do a mitered edge. Probably more expensive than the plywood, but a more finished look?

It would be very difficult to keep an existing backsplash with a countertop replacement. If you're selling the house, I wouldn't spend the money on replacing Corian with granite. You probably won't get the money back.

I think we are moving in the direction to do the island, perimeter counters and backs splash (all the way up the wall) in the same White Santorini Quartzite. Any feedback on this? Im sensitive to adding too many different materials into the mix. Is this too much of one thing?

I’ve seen the Silestone Calacatta Gold in several “I hate my quartz” threads, and I agree. It’s not attractive installed. It looks like a child’s drawing of marble, lots of huge fake veins that never line up and look stripy. There’s an active thread on this right now, I believe. The Viatera Muse and Minuet I have heard less about, meaning there may be fewer complaint threads on them. They certainly look more subtle. The key to choosing the right backsplash for these types of counters depends a bit on the color of your cabinets. Are they white or wood?