The crazy backing could be done either way - start in the center and keep adding rounds (sort of like a wonky log cabin on steroids).
Or you could just add pieces to each other and keep trimming so you have a straight edge to then add another piece.
The only word of caution would be make sure that you keep long seams AWAY from falling near where the edge of the quilt might end up after trimming.
You don't want to have to deal with a sliver of fabric at the edge and/or putting binding over that parallel seam. Not fun. At all.
I piece most of my backs. Love them.