Yea, those folded belt loops do tend to get in the way, I use a piece of leather the same thickness as the loop to back the edge of the sheath so the drill goes straight. I've got several pieces of scrap right by the press just for that. It helps a lot.
Grooving the back of the sheath does lend a lot to how professional the sheath looks overall.
I do think your quilting is good! Its not one of the easiest to master by any means, something always seems to be off.
Hard to tell from the pics, your edges are just a little uneven. If you have a belt and/or disk sander its the easiest and most efficient way to get them nice and even and vertical. It also shortens the time it takes to get them polished and edged. Before I had my sander I used a jig with sandpaper glued to a board and a 90 degree upright to help me with the angle. If I saw this wrong as a trick of the light, all apologies.