That's a great suggestion - we are new to chickens too and found that it is safest to have access to two setups in a pinch. Plus you will want to get more. That's just a given 
But I think the easiest thing would be to make a second plywood hutch like you have there, and just connect the two. You can even make a pop door in between instead of completely removing the walls, and then if you need to isolate, you can just close the door. Extend your run to match and remove the wire mesh on that side, or just roll it up and store it in the pen already connected, so it can be closed to separate the pen into two separate runs without too much hassle.