Assembling went fine, I had my machine ready to go in ~2h.
But then I started hesitating: Using the offline controller did not work (at least not very intuitively). It moved along all three axes unitl it hit one of the end stops, then nothing moved until I restarted the machine.
So I went on to find suitable software: SainSmart promoted Candle. But candle seems not to be acitvely developed anymore; the default Linux build is a 32bit one and it is quite some time ago that this was the default processor architecture. There are builds for x64, but they only contain Windows executables.
So I went over to read some blog posts on "the perfect software" and found the sentence "UGS + GRML are the standard combination for milling".
That was easy! I Downloaded and installed UGS, hooked up my machine and ran through the Setup Wizard. "No serial ports found" was what I earned. First I put my user to the group "dialout" because the device belonged to root:dialout. That did not help, so I simply changed the device to belong to my user.
With that I was able to get the Setup Wizard running and connecting to my device. But after the first step I only got a "This controller is not supported by the Setup Wizard".
So stucking at this point I realized, that a CNC machine + Linux might be a rather rare combination.
Let's see what will be next...