"He's got a bunch of software that W10 doesn't support but tells him he can 'upgrade' that software for X $ each."

I have yet to find a program that doesn't work so that's quite a different experience to mine. A quick look suggests I have well in excess of 250 programs installed and I have yet to find one that doesn't work - at random I just tried musescore, ableton live 8, dreamweaver cs3, an alternative version of Reaper and Paint Shop Pro 6. I haven't opened any of those since upgrading and they all work. Reaper which I record with via an M-Audio M-Track thing works fine. Teamviewer which I use a lot works fine and no hassle with favourites etc moving.
On this machine I don't use any 16 bit programs and have an old Xp machine if I need to

No apologist for Microsoft but have just found it all very easy and just carrying on with stuff as normal

Office 2000 is supposed to not work on Windows 8 and 10 but it does even from a clean install

Perhaps I'm lucky on the two machines I have (one old one newish) as I have colleagues at work who have had issues, but so far so good and I see no reason to go back.

I will, however, continue to manually tweak a lot of the privacy options as I am more blase sometimes than I probably should be.