Windows 10 can be installed via Bootcamp with one caveat. You will
need to install Windows 7 first, then upgrade to Windows 10. There
is apparently some driver that is installed in Windows 7 on older
machines that is not available in any Windows 10. installer that needs
to be "grandfathered into" Windows 10. Even though the Win10 installer
seems to work, on "final reboot" (there are so many) it never proceeds
to the user setup stage.
I speak from experience on this doing Win10 installs on an early 2009
iMac as well as 2011 vintage MacMini and MacBook Pro. As a matter of fact,
I have Windows10/1809 running as a sole OS on a 2011 MacMini Server
that I am using as an entertainment center.
In terms of a virtual machine environment, if you want to do anything
truly useful in Win10 and macOS simultaneously, 8GB RAM is an absolute bare
minimum and really suggest 12-16 GB for a good experience.