Agreed, this ought to mantra for everyone. Ever since XP, I have always installed or setup Windows in essentially this way—and I never do the setup with the internet connected (not even with Linux). If in the middle of the process I need an updated hardware driver then I'll download it on another machine.
Once the setup is done and the O/S configured exactly the way I want it (which often takes me considerable time), I'll then mirror the drive.
I then progressively repeat the process in stages, first with essential utilities, text editors and maintenance tools and work up to bigger programs, word-processors etc. At the end of the process I'll end up with at least four mirrors. If anything goes wrong I can restore the image which typically takes me 7 to 10 minutes and I'm right to go.
Doing the job in multiple stages is good idea if you want to remove traces of a program that, say, won't allow easy re-installation for licensing reasons. All such program are relegated to a latter-stage image, so the process then is to restore the immediately preceding one that is 'clean'.
Only when I'm finished saving the last image and I'm totally happy with the installation do I connect the internet.