over the weekend, I did the upgrade to Win10 directly into the existing Win7-x64. Worked quite OK.
Only one hard issue was to be solved (more to that further down). Also the eLicenser software was to be updated. All the rest is so far (!) working without problems. No other re-install of software or drivers was required.
The most time was spent on backing up the system disk. Did it two times with two different software tools - just to be safe.
The hardest part was to find the one (!) piece of software, that was blocking the upgrade. The Windows10 upgrade tool kept saying "It is not possible to upgrade your PC … error 0x19001… or so ". No info about what in particular was blocking this. Is it eligibility, free upgrade period closed (which is not), incompatible drivers or software, etc.
During the many tries while removing step-by-step unnecessary or questionable software or unplugging USB-devices, I kept searching the internet. Also made a deep-dive through “panther” log-files created during the upgrade. They should disclose, what is blocking the upgrade,
Found many many hints in the internet (just hints, not solutions). One of those hints lead to the solution. A Virus Checker can be the problem. Finally, it turned out, that the blocker was my virus checker (it was not Windows Defender).
Once the virus checker was uninstalled, the upgrade went through. It then took something like 1-2 hours (medium fast PC with SSD). Some attendance is required for selecting certain options here and then.
After having finished that, I plugged in all the USB-Devices and started Cubase. Only the eLicenser showed error messages. Something like “too old for this version”. Once eLicenser was updated and its maintenance procedure was completed, Cubase started without any other problems. Projects are still intact, 3rd party plugins work, all USB-connections were up and running. Looks good - so far.
Also the other pieces of software installed on this PC (not very many) seem to be OK.
Hope this helps some people here to reduce the pain points to get over it.