You got quite well through with the Windows 10 transitions - gratulations. I can wholeheartedly suppport your recommendation to move the system drive to a SSD for a good speed gain. And yes, the Win 7 updates take looong, Win 8.1 updates are already very much faster.
I got quite easy Win 10 upgrades with a few systems, older hardware as well, but got into unsolvable problems with others - one problem was a Hasp security driver for an USB dongle, that blocked already any upgrade attempt to Win 8.0, the orginal software provider for the package using this dongle does not exist anymore and there is no support, no update to new drivers etc. The removal of the Hasp software took 3 days , with tricks to remove keys in the Registry which are protected in the core system section against removal normally etc. That old software would start on W 8.1, but only in demo mode, and the internal calls to the Hasp driver, a newer version - won't work, and that software, the USB dongle would not work either in a virtual Win 7 system under Win 8. . Other problems are drivers which are unsigned, and quite tricky to activate in Win10, or not at all, or just work partially , and fail with strange errors. So my experience is pretty mixed overall, and by 2023 I probably will decommission some old hardware anyway - or earlier.