How to re-lay bedroom flooring and insulated

Looking for some advice on carrying out some works. I'm in a new build and the entire upstairs floor creaks excessively. The floor structure is made up of engineered cassettes (I-joists & a 15mm OSB deck) with 22mm Caberdek laid over it. Neither of the layers have been glued or fixed properly. The OSB is weather damaged and there's no fixings in the chipboard at all, as well them overhanging on the joists (short ends are literally in the middle of the joists) It really needs a full rip out, but being realistic, I'm looking at doing it room by room to minimise upheaval. Would it be best to cut out the full floor to the nearest joist at the edge of the rooms and re-lay properly, or just cut out sections where it overhangs, re-board and screw the remaining floor? I may as well get some insulation in at the same time while the floor is open. Would I just lay that over the plasterboard ceiling or suspend it somehow? Thanks