Have you started yet?
I'm really excited for you and know you will have an interesting time as you work on it, considering the different pics and the stories they are telling you.
Here's another idea ... would be a little less quilting but could be quite effective.
Keep with the same mullion design I suggested to frame in each block.
Still outline or echo quilt the embroidery.
Then quilt from corner to corner like an X, but not on the motif.
Measure in same distance on top left and bottom right. Quilt the line between those points. Continue on around the block with these angle lines. I'm thinking the ends would be 2" apart around the frame.
Gives you a starburst effect. So less quilting than the cross hatch.
I did this with an embroidered wall hanging with different cardinals in each block, but machine quilting. I really like how the lines draw my eyes into the embroidery and see the difference from one cardie to the next. But was quite fiddly with all the end points of the stitching lines requiring a lot of burials! Bonus, you wouldn't have the same burial issues!!