Question in short:
How to install an alternative OS (debian preferred) on a headless server and what OS to use for a home media/dataserver.
My questions now is:
How to do it?
The server will, in rescue mode, accept an PXE boot image via tftp.
But from that point on the whole process needs to run completely automatic until the point where the server accepts an ssh login as there is absolutely no possibility to hook up an display to that server without breaking it open and soldering VGA cables.
In the end I used a PXE preseeded booting… i packed the preseed.cfg into the initrd.gz file and pushed everything to the machine on netboot via DHCP/TFTP.
What you are describing is a preseeded PXE install. Just make sure you fill out the seed-file correctly (use the example) or the setup will halt.