Thank you Lew, Andy, Mike, Mallard, Dave!!
Mallard, That is a great idea to lay the plywood on foam to cut to stop splintering. In the past, I've laid 2x4s down with the plywood on top. It's not nearly as nice a cut. I have a plywood carrying tool; In fact that is how I got the plywood in the house in the first place. 
But now since I have trouble with both legs and my back, it isn't even enough.
Dave, from now on I'm going to get it cut at the store. For another thing, we no longer have a minivan. After buying the first one in '93 when our younger daughter was born, I have always been able to carry a 4x8 sheet of whatever. Now we have a '16 Ford Escape and my old '04 Sonata.
We are going to lay that sheet of plywood down and cut it right in place. Get out the 2" thick foam for the cut. 
The sections of Masonite backdrop and Homasote are small enough I was already able to move one of each from in front of the plywood with no trouble. Since I am going to build the roadbed and scenery in modules I can move to the other room later or to another house, I don't need big pieces of plywood for an around the walls layout anyway.
Thank you for all the great comments!!
