Older thread I'll resurrect for a bit of insight. I do this as a part-time business but do not consider myself any sort of expert and these are just my humble opinions.
When designing a holster three things need to be considered and should be considered in this order:
1) Safety
2) Function
3) Form
Not to pick on Eaglestroker, but when I see a 1911 with a fully exposed trigger, I almost jump back away from the screen. This fits into the safety aspect. Make sure for all but single-action-only cowboy holsters your trigger guards are covered and the leather in that area can NEVER find its way into the guard. Additionally, ensure that the handgun is well retained. Either do this through the molding process or by adding a retention strap.
Regarding function, the holster must meet the purpose of the handgun. I make leather holsters but often times wear plastic for IDPA. Why? It is what works for me. I carry leather and make sure that at least one practice out of the month I use my carry gear. If you add a thumb-break, you must practice with it. When taking orders, I try and talk customers out of thumb-breaks because I know 90% of them will not practice enough with it to commit it to muscle memory. If the holster is hard to get to or hard to pull the handgun from, it will do you no good when TSHTF. Pocket holsters are popular with the micros and work fine when standing. What about being car-jacked? How about having to take cover before drawing and crouching behind cover? Can you get to it. Some can, some can't. Consider these things when designing.
Final consideration is form. If I make ugly holsters, I don't sell many holsters so this is a business thing for me, but it does tie into the above two points for you. Stitching and molding are a part of the form. Stitching too close to the holster edge, not using a stitching groove, using thread that is too light-weight, using stitches like chain-stitches (the stitch produced with those stitching awls) will all cause premature wear of the thread. Even if you are using industrial glues (Barge Original comes to mind which you need a tax ID # to purchase in any significant quantity here in PA), your stitching is the lifeline of your holster. I did an experiment with one of my double-layer belts and left it glued with Barge Original and un-stitched. Started separating in 3 months after daily wear. Since most do not own a sewing machine large enough to handle T69 and bigger thread punching through 1/4"+ of leather, hand sewing is your only option. Diamond awl, harness needles and saddle stitching take time, but are easy to master with practice. Get the above tools plus an edge-guided stitching groover, a free-hand stitching groover, stitching spacer (pricking iron or overstich wheel), descent beeswax thread and buy or make a stitching pony. All can be had from either Tandy Leather Factory, Springfield Leather or any of the other leather supply merchants or even on Ebay (which has tools that are made much better than most produced today and will work fine with a little TLC).
Leather used should be Veg-Tanned sides, shoulders, backs, or bends (or butts if you want to get into horsehide). Belly leather will work for a bit but will soften up over time and loose the retention and drawing properties you need. Best to stick with leather weights between 6oz and 10oz. Smaller weights are to flimsy unless doubled-up and larger weights are too thick.
Again, these are my opinions based on my experiences so take the advice for what you paid for it and YMMV.