Jeff at Grey Ghost is a good guy. I've taken a carving class from him and was very happy I did. I've also had him make some maker's stamps for me. The thing about his $145 guitar strap templates is they actually make three different style of straps. If you make straps for country western players this is the one to get.
Hi Eve,
This a good book to learn about gussets.
http://www.leathercourses.co.uk/the-leatherworking-handbook/
As well as the three Al Stohlman case making books.
Good luck,
Steve