I have been working on blocks off & on for a while. As I find another fabric to try a block. It’s fun and one day will be a whole quilt. The individual blocks are terrific. As for backing for an extra large queen....???? It would depend on the size of the top — how big is extra large queen?
I recently quilted a king for a friend- it was 106” x 115” she purchased a wide backing, 118” wide by 3 1/4 yards (127”)