I do all of my pattern and mold work in SolidWorks, a 3D CAD program and then I 3D print cutting templates and molds. The cutting templates are typically 0.1" thick whith a little handle on top to hold on to them. A typical cutting template costs maybe twenty five cents to print and a three or four piece mold set maybe five dollars. I find that a lot of errors can be caught and fixed in the modeling process and the 3D printed parts are a good way to improve accuracy and speed up production. These days I almost never cut without using a plastic template to guide the knife and for molded things like sheaths and holsters I always print a mold set. If I have something I am going to make a lot of I may have as many as ten 3D printed parts, a combination of cutting templates, molds and alignment jigs.
When I am designing my templates and molds I include the pattern for any design or stitch lines in the part. The 3D printer will print a raised line on the part as narrow as 0.4mm so when you lightly press the template on the leather piece to cut it out the raised part will leave a light impression that can be used as a guide. If you want to sink your stitches into the leather you just print the raised part a little higher and press it a little harder into the leather. This takes some practice but eventually with one press you can make a groove for the stitches and a guide for sewing at the same time. The beauty of this process is that using a CAD program you can make your designs and patterns perfectly symmetrical; all of your arcs are tangent and lines are straight.