Material Question - floor repair

I have a 21 ft Winner Warrior, with typical floor construction, plywood and fiberglass overtop. The plywood has rotted out making the floor very spongy - obviously I need to replace the plywood. My question is what kind and how much fiberglass do I put overtop the plywood? I am confused by all the options - mat, cloth, biaxial, etc. I am leaning towards using polyester resin. (cost and familiarity)

Next - is there any good technique for covering such a large area (approx. 7ft by 8ft). I have never attempted to do such a large area before. Should I do it in stages?

Thanks
Doug

Material Question - floor repair