As long as it is short term and you put a couple of coats of a good exterior paint on it, sure. It's an interior grade product but with paint, it should be fine for a month or so.
Yes, they can cut it at the store. It's always best to cut it yourself but if you lack the tools, they'll do it.
This board weighs approximately 9 pounds.
I used it for garage shelving so I don't see why not.
No, I would recommend plywood instead.
I would use interior bugle head Grabber screws sold at Home depot: https://www.homedepot.com/p/Grabber-6-x-1-1-4-in-Bugle-Head-Philips-Gold-Screw-1-lb-per-Box-23205/203111650
@dougb - thanks, uniform load on the 3' between the supports. Trying to figure if it would work for a book shelf.
yes you can do that.
No Margaret, 4' or 3' is just about the longest you'll get!
ABSOLUTELY NOT! Pine is way too soft a wood for a cutting board. Use only hardwoods such as Oak, Hard Maple etc.