My very first granny square blanket was a hodge lodge of tension differences as I was trying to learn. (Not that I'm any better yet). I put on the edging before blocking as I knew nothing about blocking. Then I finally did the blocking after looking at a wavey and bubbly blanket for a few weeks and it nearly resembles a proper one.
So my advice is block as you described after you've added the edging and are finished all your hook and needle work.