Dear @Stefan_Steinbauer,
Good to have you in the community, you will find here a rich source of information and active members able to support each other. Also the Codan’s take active part, so this is the right place to be.
At this moment it’s not (yet) possible to link between different Coda documents, but: 
The Copy/ Past funtion has been developed recently quite well , so you will be able to get everything in one doc and then where necessary build the relations.
Succes on your journey,
//JP