Hi there. I've been doing stained glass for many years. Yes, you can make a window this size using copper foil. I would suggest that you choose a wider foil. I have made some very large foil windows and have soldered copper wire, which bends and twists nicely, following the vertical lines of your pattern as reinforcement. If you are still hesitant, you can divide your pattern into 2 or even 4 and use perhaps an H zinc channel and design your pattern to carry through from one section to the next. It is not uncommon to combine both foil and H channels. Hope this helps and p-ost a picture when you're done!
Q