EDIT: Okay, after some more time I got it to work by creating a new project with the template and just adding new code line by line and compiling after every line. What caused the old code you see below to crash was most likely the spawn call. it needed to be
World->SpawnActor < AActor >
(I needed to put the spaces because otherwise the text wouldnt wanna show up in the comment)
Now I have the next problem. I have no idea how I should set all the variables I need to set on spawn (because I have no idea how to tell the c++ code about which variables the blueprint class has and needs) and I slowly get the impression that it’s just a bad idea to wanna access such a blueprint within c++ code?
Old Post:
01:52, Germany here as well 
Thanks for your help. Here are the classes:
h: TwinStickCPawn.h - Pastebin.com
cpp: TwinStickCPawn.cpp - Pastebin.com
Note that I tried using
TSubclassOf BlueprintVar;
and
UClass* BlueprintVar;
in the h file, neither worked.
Thanks so much for trying to help everyone!