Hi, and glad to be of help!
1. The straps on the side are the same as the shoulder strap: 1 3/4 ". Unfortunately, I can't remember how long they were. In fact, I had to keep cutting them short when I miscalculated.
2. I'm sure I could have done this better. But I measured every 1 1/2 inches, and then removed a little more than 1/8 " of leather right on that line. Which leaves a little over 1 1/4" between each slot.
3. No, I only have the flap strap on the front, but that's not to say you couldn't have it all the way around. Mine measures 18 1/2 inches. I wove it in with the side straps, but it might look better sewn on.
I'll be interested to see it when you get finished, if you plan to share!