Actually, I'm having trouble trying to combine a func_train with turrets.
Does anybody know how to do this?

Crusard, the best place for information about Lazarus entities is the RUST forum.
But I'm not sure if it is possible to combine a func_train with turret.
I will also recommend you to test your map with the kmquake2 engine, because Knightmare has done a big job when merging Lazarus code with CTF with ACEBOT and more, but it may not be fully compatible with the original Lazarus. Try if you want to be sure.
I suspect the actual bug in mission 9 with the data spinner to be introduced by the mixing of various dll code.
There are also some Lazarus feature that are not implemented in KMQuake2 (fog, ...) because they are initially not working in multiplayer.

lemme know if you get it to work, cause I consider doing something similiar later

Apparently the func_trains with turrets don't work as long as they're moving, but when the train isnt activated the guns fire normally. So much for my battleships...