Hi Stelios_Savva,
I can see that you have already found some very good resources! Antoher resource that i have found very good is this video:
It describes many of the same things as you have already learned in the resources you mentioned but uses different sample data and explains a few other modeling ideas by sample.
Is it possible for you to try a few data models in a small PoC and use that PoC to decide what model is working best in you application?