The steel I-Beams would be the least of my concerns, it would take 20-30 years longer than the structure will last for them to rust and fail!
The ply-wood is a No No if it does not have 1/2"drywall on the walls and 5/8 on the ceiling behind it. I don't know of any reason that you could not have it if the drywall is OK, but to be safe you might want to call the local fire inspector/dept. to get their take on it.