@arup was very kind and helpful to go to his local shop twice, send pictures, weigh 40 motherboards, pay the scrap seller upfront, pack them all up and send pictures again. I have paid him, arranged for shipping and the package got shipped yesterday. (He even refunded the extra money I sent for the generous help!)
Can't think him enough, we need more people like him in this world!
Now awaiting the package to arrive, and the project will be well underway!
Planning to get a 2-inch thick and 1-inch width frame like one shown in image, and attach a single 1-inch thick sheet of plywood to the wall. Then, all the motherboards can directly be screwed into the plywood, not damaging the wall at all!