First, let me congratulate you on the quality and quantity of your work. Very fine.
The only high relief panel carvings I know were simply coated w.many layers of wax. If I remember my student instruction, turpentine is mixed w. the first coat of wax, so the wax may enter the wood grain, and then, subsequent layers of wax were laid on and polished over a period of weeks. The ends of the panels were often capped by a thick coat of wax to inhibit splitting from the end.
I never encountered anyone using lacquer as a finish. A standard finish was penetrating stain (often neutral color) and then several layers of varnish. Lacquer, when used, was reserved for furniture and small decorative works.
I suppose contemporary practice where I live now uses substances that didn't exist 40 years ago. But the older methods worked well. I handled some low relief icons from the 1600s, and the heavy wax over the ends and back had held the wood stable.