It is a little difficult to reach the very back but it could be remedied by having the cage on a shorter table. My table is custom made and 22 inches tall. I'm short as well (just over 5 feet) and I can reach, but even an inch or two shorter would be nice.
It's hard to tell from the photo but I don't have a full grid in between the cages. There is a 2 square overlap at the top. I was originally going to have a full grid in between but as I was building it I realized it was going to be too tall, so lowering the top cage by 2 squares helped shorten it a bit and added a lot of stability.
Another thing to help is having doors on the front of the top cages. I have these V-shaped Springs and latches on the front to form doors so it opens and I can reach. If it didn't swing open, I wouldn't be able to reach the back.
You don't have to use grids for baby proofing. You could make your coroplast trays have higher sides and cut them down later. Or you could just punch holes in and zip tie on some cardboard.