We manufacture leather working machinery. If you're making hand tools, I think a lot of it is going to depend on the design the maker wants to produce. It's very reliant on their ergonomical opinions and how they are trying to shape and mold the leather. Some of it is just going to involve taking an informed stand because the industry is very much full of stubborn opinions about which way is the "right" way to do something.
There's also a lot of paranoia involved. My dad got into saddle-making out of high school and found that most of the old-timers were very reluctant to share their wisdom because the "new kid would steel their business." There's still a fair amount of that today unfortunately which means that there's even MORE people doing things their own special way. My dad worked his way up from knife sharpening in the old saddle shops and eventually got into custom harness making and repair. having a broad knowledge of the leather industry will be a big help. You and your customer will need to do your research and determine where you sit.
The metallurgy side of it isn't very complicated. Most blades were originally Case hardened steel and as time went on, some switched to O1 tool steel or High Speed Steel. We've found that A2 and D2 work well for a lot of applications. Like all hardened steels, you'll need to find the balance between wear-resistance, flexibility, and stability.
The actual machining will likely involve lots of hand finishing and polishing. I doubt you'll need the volume necessary to justify automation, and lots of users prefer having tools made the same way they are being used, with care by hand.