High quality MDF -- the top and bottom surfaces (1/8") seem receive an additional pressure process making them "tempered" like tempered "Masonite"
The 12 inch x 72 inch was approximately 25 pounds
It would depend on the support spacing
The one I purchased was 12 inch by 72 inch. There may have been different sizes.
It is my experience from past purchases that you get one cut for free and pay for additional cuts.