I am kind of answering my own questions here now, but it might be useful for someone else.
 
The reason my z3950 server didn't behave properly seems that in my imported biblio there were some author names with quotation marks around them and some that had not. (Don't ask me why, I have no clue)
I removed all quotation marks and re-imported my list, and it works well now. Pretty cool, I would say.
 
Only one thing; I still have to start it manually. Is it supposed to start when Koha starts, or when you start a search?
 

Marty Jongepier