Bert,
Having made quite a few holsters, I offer the following as suggestions.
Stitching: Get a set of 4mm lacing chisels. Cut out your leather and tool it (If desired), dye it then lay out your stitching line. Use the chisels by placing them on your stitch line and then using your mallet use them to pierce the leather. This will make your stitch holes evenly spaced and properly sized along the stitch line. For the actual stitching, you will need a clam to hold the hold the project along with two needles and thread.
Assembly: After finishing your stitching, submerge the entire project in warm water for no longer 10 seconds then sit aside until it appears dry on its surface. Then fold the holster body through the loops and if desired, insert your pistol (wrapped in plastic) into the holster and work the leather with your fingers and thumbs to mould the holster to the gun. Leave the gun i the holster over night until the leather is completely dry, then oil and wax the leather.