Is it possible to run Windows in KVM, without the extra GPU or KVM switch, but with degraded performance? Not for gaming, but for example for Office use?
yes you can, (Atleast if you can handle the extra CPU and Disk I/O). I think you should checkout winapps [1] which RDP's into the vm to give you a pretty seamless experiance.
P.S. Disk I/O can be a severe bottleneck on HDDs, so try this with a SSD.
Yes, QXL can do that and has built-in support in e.g. virt-manager. It's not going to be fast, but it does work, and is how installation of Looking Glass can be bootstrapped without a physical monitor attached.
P.S. Disk I/O can be a severe bottleneck on HDDs, so try this with a SSD.
[1]. https://github.com/Fmstrat/winapps