Metal roof over timber structure

I get a lot of conflicting information on the type of roof I should install on my new home. It is a timber structure that I plan to first apply 2x 6 t&g covered with ice and water shield Then I planned to lay down osb screwed through the 2x 6 into the timber truss. This would address the diaphragm effect of just the 2x6. Then I would install 2 layers of 3 inch polyiso with staggered seams. I then planned to lay 2x4s flat directly over the timbers.covered with 5/8 sheathing. These would be screwed through the entire system into the timbers. The 2x4 between the foam and sheathing would allow ventilation I was not sure of the added advantage of then installing horizontal 2x4s . across the vertical 2x4 so I left them out. I would then cover the 5/8 sheathing with 15 # felt and finally the metal roof. Is this system OK