Welcome to the forum. I have made 2 avenger style holsters. I will eventually make another one, hopefully better this time.
Like you, I bought a 4 prong punch and only used it once, luckily on a test piece of leather. Now I mark with the overstitch wheel on dampened leather, and since I can't see the holes, I use an awl to make each hole visible. Then I drill with a dremel tool and 1/16 bit. I tried smaller holes, but it made lacing more difficult.
I just bought a drill press and next week will buy a belt sander. I am also making a burnishing tool using apple wood, but I can't get it fully round, so I will ask a co-worker who turns pens if he can finish it up for me.