Thanks for the tips and encouragement, jweb & DD. I made the loop this morning and I'm pleased so far with this relatively easy part. The right side of the first pic shows my machine-stitched seam. I used something called "extra strong nylon Upholstery Thread" made by "Coats & Clark". Bought it at Walmart, so it should be good.
"ART-AD64-18" was the only number on it other than the SKU. My wife said it was thicker than what she would normally use on her household machine. and I couldn't break it with my hands. I showed it to a lady at Joann Fabrics and she said "that's good stuff." I wish I would have read your post first. I would have used a longer stitch length. I'll probably scrap this first attempt, so I can do that on the second try! (...or third, or fourth...)
The hand stitching will be done with thicker "Bonded #277 Nylon...for Upholstery Outdoor Leather Canvas Bag". It's what the YouTube video said to use. For those who are crazy enough to try this, here's the link:
https://www.ebay.com/itm/Bonded-277-...item3cd27ca6e1
I made the gang punch in the third picture so I'd be able to get even spacing. I'll break that down to a two-hole punch for the curves. I'm going to try following that with an awl, but if that's not a big enough hole I'll get a HF leather punch.