Made the jump too and it was the reason I was offline for a day or two
Initial upgrade from Win7 Ultimate to Win10 Pro went pretty flawless.
I read I had to upgrade first to then use Win10's own app for resetting your machine.
This allowed my machine hardware to be registered first so that you won't need a Win10 license key when doing a clean install.
So I made some backups (forgot TG key of course haha) and pressed the "reset" button in the app.
All went fine until after the clean install Win10 did not recognise my SSD as a boot device anymore.
In the end I fixed it by downloading the Media Creation Tool from MS and created a USB boot device with that.
Took about half an hour, but it worked very well.
Inserted the USB and followed the installation procedure.
Activation was automatic.
Now I'm on Win10 Pro, fresh install and it works fine.