You will need a metal fabricator to custom bend the piece out of brushed stainless, and make sure it's deburred. It's not DIYable unless you have a good sized metal brake and are pretty experienced. As to what shape you would need, you need to do a template out of stiff cardboard and get that worked out before you take it to the fabricator. You want a bit of a slope from the backsplash to the insert, with some flanges for attachment. You would join it to the insert with sheet metal screws or rivets. You need to take into account what type of backsplash tile you will be using to get the angle right.

As far as behind the stove, you can do stone or you can do stainless. They'll be about the same cost and same degree of difficulty to install.

Cardboard! Good idea. So it would slope from high (3" away) to low (against wall)?

I am not sure about the SS on the counter. It has to go straight down the wall 6". Would it be a separate piece on the counter? 36" by 3"? Not attached to the other piece of SS?

Peke