Hey Peashooter Joe: I'll just run through a few ideas. 6 oz leather is pretty heavy for a hunting pouch so forget the lining, it will only addd more bulk. You can soften up the leather by rubbing it over a rounded edge of a board in a shoe shine fashion. On heavy leather the gussett is mandatory so that is a good idea, taper the sides of the gussett up to the flap so the flap fits over the top of the bag. Tandy sells a hole spacing tool that rolls along the leather, such as 7 holes to the inch. This tool doesn't make the holes, it just lays out a good spacing pattern. You use a small hand awl to make the actual holes in the leather. Then use waxed linen thread and put a regular needle on either end of the thread and lace up the bag in a shoe string fashion, going through the same hole with both needles but from opposite sides, this leaves a solid line of stitching on either side(its called a saddle stitch). Sometimes it will be hard to pull the needle through, even though you made a hole with the awl, use pliers if necessary.
Good luck- if you have more questions-ask.