I can't tell how you have the posts set. Are they in the ground, or on top of the sono tubes?
If they are in holes drilled into the ground and they set with concrete, you don't need anymore bracing. Bracing is to stop racking. The posts in the ground won't rack because they cant. The ground is doing all this for you.
If the posts are on tope of the concrete, then you need diagnal bracing from corner to coner. The bigger the triangle you create, the more strength you will have. If it was me, I'd bolt on some 5/4 PT decking for bracing it. 8 boards going in both directions from each corner will make it totally solid.
Nice project!!!!!!!
Eddie
