+1 to this. KVM and virt-manager Just Work for me on Debian 9. I don't know what I was doing wrong with previous releases but I just installed it, added my user to the correct group, and there I go.
Have you gotten Windows to work well as a guest?
I could never get it to work as well as it does with VirtualBox.
I don't know about working as well as it does in VirtualBox, but with the QXL guest driver to do screen resizing and clipboard sharing, it's not too bad.