This seems problematic. The problem is that stretched canvas sags and the weight of the canvas will cause it to sag and get loose. The larger you go, the more potential there is for the canvas to get loose over time. With something this big, I would look for a way to mount it to a large cradle board. Chances are you'll have to make your own cradle board to make it work.
If you look at huge canvases in places like Le Louvre, or the Mucha paintings in Prague, you will notice they all sag, and they're all a bit loose. That's acceptable for a historical piece in an internationally recognized museum, but a new canvas that is meant for decor, will likely result in complaints, especially over time.
For something beyond 48"x92", or 4'x8', you're not going to get a single piece of wood to mount it to. You'll have to use more than one panel, and then probably join those panels with wood putty or something, then sand them so that the seam doesn't show once the canvas is mounted.
This project sounds like it's fraught with issues and I honestly wouldn't want it. If you do it, you should charge a lot of money - far more than normal, because this one is going to take some serious time and effort, and if... if you have a print issue at all, then you've just spent a ton of money on canvas and ink. And of course, how on earth are you going to UV coat that thing?