Also: do any of you know, why space stations have no armour and can only mount civilian components?
I'm actually unclear on the first question, but for the second the idea here is that the "No Armour" checkbox means the space station can be built from planetary industry. Mainly, this is a concession to allow building massive industrial platforms, maintenance stations, or Ark Modules without having to expand a shipyard to 100ks or millions of tons.
It is still possible to build a military space station, it is just a ship class without engines - but you have to build it from a shipyard. Sadly this is less flexible than PDCs from VB6 but it is what it is.