The average desk is about 30" tall and the average jeweler’s bench is about 38" tall. That said there is no right answer with bench height. It’s definitely a matter of personal preference, including how tall you are and what kind of chair that you have. Many folks who build jeweler’s benches out of desks create some kind of risers to raise up the desk height.
I know for me I like having options with working height. I rely heavily on the GRS adjustable height bracket.
Another factor with a desk is creating a catch tray. There’s been a number of threads talking about different ways to create that.
Do you think that you want to make a circular cut out to correspond with whatever you use for a catch tray? That will be another decision.
Most desks have a thinner top than jeweler’s benches. GRS makes a steel mounting plate for this situation. You’re pretty innovative and will probably want to make your own, but this is what I’m talking about.
Here’s a couple of old threads about making a bench out of a desk.
Looks like a beautiful desk! You’re going to have fun with this!
Jeff