Reply by Gregn

The 4×4 posts should be sufficient for carrying the load. Don’t set your post in concrete they will rot quicker. Set your post with pea gravel instead, this will allow for moisture to drain away from the post. The 5/4 pressure treated deck boards will warp and twist as they dry out with out solid support. My suggestion would be to use Cedar fence boards instead. 1. They are lighter. 2. They will warp and twist very little and last a long time with minimal care.

-- I don't make mistakes, I have great learning lessons, Greg