Why would you use anything but XP if that's what the machine came with and your software doesn't need windows 7+?
Also I'm guessing that the tablet doesn't have a DVD Drive, in which case you could create a bootable flash drive. Build 10586 can automatically detect a Windows 7 or 8 BIOS certificate and automatically register your copy of windows 10 without upgrading.
Everyone who works in IT knows better than to use an in-place upgrade. Use it to register your hardware id with Microsoft and then do a clean install. It will be much smoother. And you can skip the Microsoft hotmail Id, just choose other, etc... They hide it but it's in there. Just keep looking for it.
And Microsoft is only offering a year of free support for those users