Regarding tire width and pressure, I learned a little lesson on the 120 mile gravel Denali highway a couple years back. Just drifting from one tire track to another was enough to cause my wheels to slide right out from under me. I was rolling a 700x41 Surly knobby on front, a 700x35 Clement pavement tire on rear, with probably too much air in each case. That was my introduction to gravel. Fortunately, I had tights and long sleeves on, but got scrapes from ankle to shoulder through the clothes. I called it a learning experience, and bought a plus bike for future bikepacking adventures. But I understand wanting to use up the tires you have, first.