I started out by drilling holes at each corner of my opening and then used a very narrow handsaw to cut through the MDF.
You know how people say they can't cut a straight line? I'm one of those people. With a scissors I can usually follow a drawn line at least. With a handsaw? No. Not a chance.
The good news is that when I put the windows in they line up nice and square and the goofy holes are hidden by the trim. And I don't need to cut any more holes. Yay!
The fireplace will be centered between the two smaller windows and the built ins will be just below them. The larger window is just inside the bathroom. I'd gotten a bunch of that size in a lot on Ebay. I've got some of the plastic 'water' that I'll put in the windows so no one can see in.
For the exterior I've got my stone for the wainscoting. My plan is to take the Grey/Brown Cut Stone Veneers and mix them with the Brown and the Grey. So I have a mix of all three colors.
The chimney is my other concern. Not sure if I want to use the same patterns of stone for it. Colors yeah, but maybe in fieldstone shapes? Something to think about.