It's 48" x 96" or 4' x 8' near exact. My HD store can precision cut these to 1/16" accuracy if desired.
I assume you are using corrugated plastic sheets instead of 3/8 plywood with a rebar stake. Corrugated plastic sheets are not nearly as rigid as plywood. Using corrugated plastic I would suggest using vertical wooden stakes at each end and possibly one in the middle. Attach the sheet with screws and a large washer.
No, we have not heard of anyone using this material for this application.
I would use glue. Just be sure that it is compatible for use with plastics.
Yes. We used it to insulate the bottom of an RV and the span was wider than a door panel. Worked great even after 2000 miles of travel.
Not if you want to keep them safe from raccoons and other predators. This is a very light "plastic cardboard". It is like using corrugated cardboard except it's waterproof. Also, it will degrade in sunlight.
Yes, that's what I use. It does wipe clean and holds up very well. So much cheaper than ordering pre-made. Have to score the lines before folding. Need shears or heavy scissors to cut.
Yes. Just like cardboard, but plastic. Consider using cardboard as a template first.
Yes. It is really just like corrugated cardboard, but tougher. I've made boxes with doors that are created from a bend.