No the trellis is on the front of the house. It is designed to shade the exposed southern windows in the warm summer months but leave a clear view, and allow the sun to come in in the winter.
I've also wondered about the concept of filling a hole with crushed stone in certain environments. The site I'm working on is pure sand so I'm not concerned with making a "crushed stone bucket".
I like your idea of the 2" foam. I think it would work quite well in an environment that has many freeze thaw cycles. We don't get a lot of that here. It often takes till May for the ground to thaw and by then it is usually warm enough not to freeze again.
I'm told by a local that has been supplying cedar to this area for many years that the posts will last 50+ years if packed with crushed rock around them. Although the raising of the bents would be much simpler with a little concrete poured to elevation, I may skip that step to avoid a place for water to pool at the bottom of the post.
The frame is designed with 6 posts and 14 knee braces both because the client wanted the knee braces and because it will stiffen the frame from one post to the next. With the joinery any post that wants to heave will have resistance from its neighbouring posts.
