No, no. no need to be sorry - thanks for your great and swift support!
30% CPU load is on my HOST (because there are other VMs running and that server).
My NCS-machine now still has a high CPU load (screenshot), but as soon as I can abandon the webcamXP service and do not run the NCS client on the same machine - I guess it will be fine (if you are interested, I can keep you updated on that).
Regarding USB cameras: yes, thanks for your tips - but USB is exactly the reason why I do have my cameras connected to other PCs: Hyper-V does NOT (not yet, even not on Server 2016) support USB ports - unbelievable, but it is so - great, well done Microsoft.
So I have connected two different (different drivers) USB cameras to real hardware physical computers. These computers act as "camera servers", i.e. they only provide their stream into my local network.
My webserver, however, is a VM and it "collects" these four streams (two machine with two cams either) plus a real IP camera's stream (so, five in total) and bundles them on the website. If you want to have a look, I can provide you the address plus test credentials via PN.