I prefer a size 90 Universal sewing machine needle for most construction. A leather needle actually cuts the leather and leaves a larger hole in the skin. If you are having problems with skipped stitches, try using a larger Universal needle first before going to a leather needle.
100% polyester Gutermann all purpose thread is suitable for sewing with leather. For handbags I prefer to use 16 weight Quilter's Silk from Superior Threads, because it stitches beautifully in both the top and bobbin threading. It is a more expensive choice, but may be worth the investment to achieve professional results. For most handbags I order 4-6 spools depending on the amount of topstitching required.
For hand-sewing use a Glover's Needle, which has a very sharp triangular point. If skins are thick and hard to penetrate with a hand-sewing needle try using a pair of surgical hemostats or needle drivers to push or pull the needle through the leather.
Unlike fabric, it is impossible to pin leather without leaving holes. Instead try using Clover Wonder Clips, coated paper clips or winged paper bulldog clips.
A rubber mallet and wooden board are used to flatten thick seams. Rubber cement works well for gluing seams flat. Double-sided leather tape comes in 1/4" and 1/2" width, and can also be used to hold seams flat. Do not use leather tape on seams that will be topstitched as it causes skipped stitches. Rubber cement is fine to stitch through.