I’m not sure what OP is trying to create, but most Internet-in-a-box projects I’ve heard are trying to recreate text-centric sites offline (Reddit for example). I doubt they are trying to create an offline version of video sites, like YouTube. The size requirements alone make it unlikely.
If you have space or an extra drive, you can always make a backup image of your Windows install and save that as a backup. If you find that you need Windows again, just recover the Windows backup image and it’ll be just as you left it.