Themken: If one builds a desktop computer or asks the shop to, it does not automatically come with any operating system. This needs to be solved in one way or another.
1) Buy Windows 10 Home retail for €140 or save a tenner and get an OEM license for €130? The problem is that is quite a bit of money.
2) Install a retail copy of Windows 7 Home Premium 64 bits in a Virtual machine inside a Linux distro? I have never done anything with VMs but read that advanced access to the graphics card is a problem and that you need a bit more RAM. Would I need to go from 16GiB to 32GiB? Win 7 leaves out a couple of DX versions and it is not going to get better going forward.
3) Keep my old Windows 7 computer alongside a new one and install Linux on the new one. Crawling behind the computers on a daily basis is not an option so either double up on monitor, keyboard and mouse or get some switch box. I am sure such exists but at what charge? Annoynig to need two big cases.
4) No Windows at all. <gulp> Both Linux and Wine and DXVK have advanced in large strides but I am sure this would still leave me with 10-30% of my games unplayable or nearly so.
Some thoughts on some of them:
2 has the downside that VM's generally have poor, if any, 3D support (unless you manage to get VGA passthrough working, but that's not for the faint of heart and it requires you to choose your components carefully). If your main reason for Windows is games, I would advise against this choice.
3. I noticed that a store was selling a 4 port HDMI switch for $40; also, you could look for a TV or monitor that has multiple inputs (mine has 2 HDMI inputs, one that I use for my PC and the other is used for various other things, like my mini PC, Raspberry Pis, and Mini NES/SNES). For keyboard and mice, connect them to a USB hub and just move the hub to a different front port each time you want to switch computers.
4 is the approach that I personally prefer and use.