New project. Need some help with floor.

[GLD]

I don't know if this is the right forum for this post or not.
Im new to this site and to boat ownership so im learning as i go. I am well trained with power tools and have some experience with fiberglass from installing FRP at work. So this should not be to bad to pick up on. "I HOPE".
I picked up a 86 celebrity 225 cuddy cabin boat last year for cheep money to tinker with. Well the floor felt alittle soft in one spot in the rear. So i decided to replace the floor. When i took the carpet up i noticed it was alittle more than the plywood that was damaged. ( Typical story right). The double layer sole support is rottet by the bulk head in front of the motor. It's not the set the motor is mounted on. It is the taller one's that the floor ( SOLE ) is mounted to.
Can any one tell me what type of wood was used on the 86 celebrity 225 boats? I can't really tell because they are glassed on the sides. They look to be 3/4" by about 8" tall. I tried to look up some way to contact someplac associated with Celebrity boats because they are not around anymore but no luck.
What is the differance between type
ABX marine plywood and CCA treated plywood or are they the same. I can't seem to find anyplace around my area that has CCA treated plywood.
What would be the best material to cover the new sole support with when i install it? The other side looks good it must have been sitting at an angle for some time i guess.
What would be the good to cover the new plywood with when that goes in? and should i cover the botom befor it goes in?
I have more questions i will get to on a later date. This should get me started on the floor.
If you use say 3/4" plywood how do you make the pcs. longer than the 8' sheet? Do you stager the seams on the doube layered stringer?
Any help woul be great for the new guy.
Thanks for reading this and i look forward to some experienced help.
GLD