Any clamp should work. Technically I use an F clamp but basically that video is what I’m talking about. If you let the leather dry while clamped then it should effectively be permanent. The only issue you might run into is if the wallet doesn’t readily absorb any water due to the finish.
You can see the process I use in this post. You don’t need the acrylic plate I’m using. That’s just to help me with alignment.
No, I mean flip the image horizontally like you are looking into a mirror. If you don’t do this then the letters will be backwards.
For the stamp I created in the above post I did also cut the letters rather than the stamp so that the letters are raised. You can do it either way depending on the look you are going for.
For settings I just used PG medium acrylic and set it to dark engrave. Last night I did two other stamps for a custom job and actual ran two passes on dark engrave because it used thin lines and I wanted to make sure the raised part was deep enough.