A friend has made holsters for some time for his own use, and made me a few, hes made some very good ones, they look very consistent. He uses an overstitch wheel I believe, to lay out the hole spacing evenly, and an edge grooving tool to make a line to follow and make the thread be below the surface level. He also uses a drill press to make his holes. Glueing in the welt and edges helps keep it all even while stitching, and a drum sander in the drill press makes a nice even edge when done stitching. An edging beveler (like a little skiver) helps get the edges cleaner looking, and a burnishing tool chucked in the drill press makes the single thickness edges very clean, I believe he also puts a touch of beeswax on the edge hes burnishing.
I made a few, but didn't go to the levels some have. Its fun making your own holsters though. Youre doing pretty well. Like anything, the longer you do it, the more you learn.