I don't know man. Custom built gravel bikes are a total fad. A bad mountain bike and a bad road bike. It doesn't do anything well, unless you are going to race cyclocross, I'd go with something else ...
If you want to have fun with a nice piece of equipment that you can customize and that also rides well, I would recommend you go with a classic or modern classic. Build up an old steel frame etc.
I am happy with my choice of the Colnago C50 I bought 2 years ago on CL with the help of my PPOT brethen. Fraction of the cost of any custom or even cheaper than a decent new road bike. It was one of the best bikes money could buy 10+ years ago and it turns heads all day long (by the people that know bikes). I had it fitted, put a new handlebar and saddle, and I am tearing it up in style.
Next thing you are telling us is that you are growing a handle bar mustache and buying tweed knickerbockers ...
G