ok, issue. You never insulate tight against wood roof decking. You trap heat and moisture underneath and rot it bottom up.

IF you planned to run a metal roof, you remove the plywood and nail the metal straight to the joist.

If the door is a 36x80 then I see you having headaches with this setup. The rack is too tall. With tubs on both sides(of the door) you will have huge diffculty sliding a tub out full of rats and dealing with them. Small mortar tubs are 28" long. That only gives a 8" buffer when cleaning or removing the tub.

If you don't vent high, you will not bring in fresh air from below. You must cause it to naturally circulate. The power vent idea is not efficient and only MIGHT work.

Drop the top tubs from the rack. pull the insulation from the peak and create an attic. Add gable vents and then floor vents and you should be good.

I avoid power use whenever humanly possible.