As you do a few more sheaths you'll gain confidence in using a narrower welt. That comes with practice in getting the stitch line more uniform and at a comfortable distance from the edge. Keep in mind that you only need maybe an 1/8" of solid welt material to protect the stitch line from the sharp edge. The round awl will help to relieve the back side of the hole for sewing and you can sure use the diamond awl the same way. If you're using an over stitch wheel to mark the holes, use it on both sides starting at the same point. That will give a solid point of reference for an even line of stitches front and back.
Forgot to comment on the glue issue. I use Weldwood low voc water based latex contact cement for all glue ups. It's the one in the green labeled can. Can be a bit hard to find, but Ace Hardware, Lowes and Home Depot usually have it in stock. Cleans with water, thins with water, no odor and no light headed feeling from the fumes after a long glue session. Several years ago I had a really bad health scare from the regular stuff after two days of extended glue ups and have used the green label ever since. Apply it the same as Barge or regular Weldwood, but only one coat. Let it dry thoroughly and glue the pieces together. Light tapping with a flat object or rolling with a large dowel sets the glue line.
Thanks for the tips .