I would use size 138 polyester thread, which is about as heavy as the average industrial sewing machine can handle comfortably. Size 217 is just a hair too big. Polyester thread stands up to UV rays better, and is better for stitching that is outside a lot.
The largest needle you can use is a size 24. A size 22 needle will work fine. If you have a Singer 111W or a knockoff of it the needle is a 135 x 17. (The first number refers to the metric diameter of the needle's blade between the scarf and the shank, 135 hundredths of a millimeter, and the second is the U.S. designation, 17 thousandths.)
No one lives forever, the trick is creating something that will.