One board weighs approximately 33 pounds.
Not treated but all in all nice quality lumber
Without knowing your load requirements that's a tough question to answer. But I use 2x10's on a regular basis to shore up decking. Might wanna consider Pressure Treaded if its gonna be subjected to the elements.
No, this is not FSC Certified. Please contact the ProDesk at your local Home Depot - they can order it via Special Order, if needed.
If you only need a handful of pieces then you can take your time and hand pick nice pieces of lumber. You would be fine. But if you were buying in quantity you would tend to get some knotty pine for sure.