IDE setup to edit xtext files

Hello together,
I try to extend OpenHab2 with an Access Control while writing my master thesis at university.
At the moment I’m trying to understand parts of the OpenHab/ESH Code and got stuck at the point the *.items files where read.

I noticed that at this point xtext is used to parse these files, my question is how to setup my eclipse ide to make changes to the xtext files (e.g. to add a user role/group) to the items. I already installed xtext and imported the missing projects, but they are full of errors (missing references, etc.) and once I include them in the run configuration OpenHab starts throwing exceptions. How can this be fixed?

Thanks in advance.