I would start with graph paper. Draw the size of finished quilt.
Make a note of how many blocks in each size.
Then draw the 20 inch square(s) followed by 12, 8-9 and use the
6 and 2 as fillers. You might have to move some around.
Make sure you have a way to sew them in rows or columns or break
them in chunks. Then place the blocks on your design wall.
Hope this helps.