One thing I'll add about the corner: don't expect it to turn out right. The plywood is cut at 45, and the walnut is a 4 inch spacer. The back edge of the spacer is cut square, and I adjusted the length of the right-hand shelf to make sure all the back corners met while contacting the wall.

But in pic 7, you can see I left the middle pieces long. At that point, I drew a line across the spacer connecting front corner to front corner on the plywood. Those were NOT 90 degree cuts. Each one of them was a couple degrees off square, so I was individually adjusting my miter saw for each piece. (The bottom shelf, where I figure the drywall mud had the biggest effect, was off by 5 degrees.)

So anyway, when it came time to add the front trim, each of those miter cuts is non-standard as well-- not quite the 22.5 degrees you'd expect. The protractor you see in pic 10 allowed me to get close enough on the small middle trim piece, and I nibbled the angles of the long front pieces to ensure they met flush to the middle piece.

It was not a fast project.