Several different points:
1) I have also been told that attic insulation *can* store BTUs, by no means do I consider that I know enough on this topic. Since it is a solid material, it seems clear to me insulation must be able to store *some* heat. Perhaps if I had some idea of how the specific heat or other qualities of that insulation (how many BTUs to raise its temperature 1 degree) that would make the truth clearer.
2) On whether a power ventilator sucks interior air from the house, it seems to me probable that is unavoidable unless you have *no* leakage between the attic and the ceiling. For example if you have 50 sq.in. leak at the ceiling (easily obtainable) and 450 sq.in. soffit vents, then one would expect the leakage to be 90% from outside air, and 10% from the house interior. Does that make sense?
3) Has anyone referred to standards of ventilation area for attic soffit and attic ridge? I tried to follow this thread but don't remember that. I have seen a recommendation of 1 sq.ft. of "net free area" per 100 sq.ft. of ceiling area, along with the idea that oversizing that vent area is a good thing (assuming you won't go with the conditioned attic design).
Best wishes -- P.Student