just one question...
a hdd I had bought much earlier, 10.3.9 Panther-Server installed on it already.
I'm not sure upgrading whether to 10.4.8 Tiger or leave it as it is.
Which one is better, Panther-Server or Tiger on Sawtooth?
Tiger will be faster and is more advanced/secure. That is what I would do anyway.
You don't need the server version for a file server at all.