I can't imagine you'd be able to use i3 for your windows apps from what I've read, but it should work with your Linux side.
Yes.
This will be available in Windows 11, so your processor does have to be able to upgrade to that. If you're fine with an OS reinstall there are ways to force the install.
I don't think he is referring to an i3 processor, but rather https://i3wm.org/