In most cases they will make 1 or 2 cuts at no charge. You really need to call your local HD to verify their specific policy since not all locations are the same.
A 4x8 sheet of 3/8 plywood is approximately 34 lbs.
I do not believe this can be done via online services.
Yes I used it for a floor
It is .375 inches thick.
Yes, nothing in my neighborhood.
no this a interior grade plywood so it is not treated
Yes. Find an assistant in the wood dept and ask them. They will gladly cut the sheet to any sizes you may need but there could be a small charge for this service.
The Associates will make cuts for you but they won't be custom. They may be able to do this for you at the moment but if it's a lot of cuts they may very well charge you a small fee.
When I ordered mine I had to pay shipping and my order was about $1900.00, if you pick it up at the store they ship to the store for free but that's it.