Trying to install High Sierra on Mac Mini 2011

I've purchased a Mac Mini 2011 for a nice project I'm working on. The previous owner had troubles deleting his info and he deleted the complete Macintosh HD with the OS on it. Now the machine boots up in recovery mode after a LOOONG white screen with Apple logo and a short black screen with Apple logo. Recovery mode is from High Sierra.

I have tried installing a new OS from within the recovery screen, that is the advised way. First I selected my Wifi network and verified that it works (I tested this with Safari and was able to open sites). Then I selected Install macOS High Sierra, Next, and after a couple of minutes I get an error message "Can't connect to the recovery server" (I'm translating from Dutch). So that's a no go...

Then I tried installing from bootable USB. I had an older HS install file on my NAS, I downloaded a new file after the first didn't work and tried creating the USB's with terminal command and with Macdaddy's Install Disk Creator. None of these three USB sticks come up when I try to select an alternative boot disk. Using the Option key to select which disk to boot from doesn't work either: the screen to select simply does not show up?!

I'm beginning to wonder: is my Mac Mini of it's drive malfunctioning? Is there a way to install High Sierra "brute force" ;-)