If this is for a bed...I too would have odd number of blocks..say 4 or 5 across..then 5 or 7 down. As far as sashing..I like the pattern to meet the edge of the bed on the sides, etc. Therefore, I will figure my sashing so the measurements accomplish this. Then when you add the border...it hangs over the bed but the quilt design is on the top of the bed. I hope I've explained this right.
If you think the border is too wide..I like to add say a 2" or 3" border than use the fabrics in main quilt and make a another small 1'2" strip around that and then add another border to reach the length you want to hang down the sides.