The ideal height for built in sitting is 18 inches.... the top "sitting board" appears to be a 2x6 and the "side posts" are 4x4. The raised boxes look to be about 5' x 10'.... there is no set dimension you need to follow. If you are planning on constructing raised boxes, do a little mock up and test how far you can comfortably reach the center of the box. I happen to be 6'4" with long arms and can easily reach the center of a 6' wide box, that may not be the case for some. Happy gardening and good luck! ~ Glenn!

The boards are true 2 by 10 rough cut cedar for a total of 20"

Also, I see what appears to be metal edging on the borders? Is that right? How do you anchor that into the ground and prevent expansion/contraction from the weather?

We do bury them so they do not bulge out from the weight of the soil. They are pressure treated lumber so they are meant from ground contact.

We like to do a minimum 3' wide pathway so people can use a wheel barrow in between the boxes.

Assuming that's a bush squash and 2x12s for the raised beds, looks like about 3 feet.

Like Rob said, make the paths big enough for your equipment, whatever that is.

We use rough cut cedar and line the inside with pond liner for protection from the soil. We also like to stain the outside so they last longer.

They are 4' by 8' and we do install drip irrigation from the bottom before we place them.