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.

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.

I don’t know for sure, but I think they generally refer to archives of specific websites that would be good to keep in case of an apocalypse. The thing that comes is the Wikipedia archive that is, at minimum, text-only. Not sure which other website archives people like to keep in case the Internet apocalypse.