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My home's insulation is totally inadequate. It has some sort of blown in cellulose fiber insulation. When I moved some of the laid in place pieces of plywood looking for a wiring fault, which I found by the way, I saw that the grey white fibers are now compacted down to 2 inches at most. Is it possible to vacuum that stuff out or will I have to remove it with a dust pan and trash bags. I need to replace it with new insulation. The 5&1/4 inch stuff is only R23 right. Challenge is that I'd like to retain the storage area up there but that would mean adding on to the height of floor joist in the attic to get to the 10 inches of insulation thickness needed for the recommended R value for zone 4.

Second issue would be air leakage. With just 3/8 inch sheet rock on ceiling joists between the top floor and the attic how does one seal the heated air out of the attic? Do I foam around the ceiling lighting outlet boxes, gasket the fixture canopies to the ceiling, or what? All of our luminaires on the floor beneath the attic are surface mounted over flush mounted lighting outlet boxes. There are no other holes in the ceiling. The heating and Air Conditioning vents are just above the baseboards and ducted from below. Since the house is half brick & block, with only the 2nd floor's walls wood framed, those walls are effectively Platform Frame as they have a sole plate and double top plates and are also fire stopped. The floor joists sit on top of the masonry walls' sill plates and a center line bearing wall on the first floor. The Second Floor walls sit on top of the floor joists. Given that and the as yet undisturbed blown in wall insulation I cannot think of any other place that would provide air leakage into the attic.

Third question: do I need a vapor barrier? Short of pulling the ceiling down and putting up plastic before hanging replacement plaster board how would I keep the moisture from the living area out of the insulation. Do I need some sort of moisture barrier on top of the insulation to keep the humidity from condensing in the insulation during cooling season. Would I need to roll out Tyvek over the tops of the joists before putting the attic floor back in place?
Yes the cellulose can be vacuumed, it is blown in, by a reverse vacuum machine.

After removing the cellulose, I would try to use a good foam machine, to save space for storage above.

You can fill the cavities, with foam, and even up to a 2X6 sistered to the ceiling joists for added R value, if desired.

And the foam will be your moisture barrier, and air barrier.

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