The Roman culture makes it difficult to mod factions if you do not want to have multiple Roman factions.
This is the big good reason I thought must have been leading to this swap... Indeed it could hardly have been a better one....

3. You can't have new resources. You can only edit the existing resources.
The maximum number of hidden resources allowed is 64.
4. Hidden resources can't be described. Or do you mean something else?
Actually I am precisely interested in hidden ressources. Normal (= trade) ressources are "defined" in descr_sm_ressources.txt, but there is no such thing for hidden ones. Does it mean you just put them in descr_regions.txt and EDB.txt and shaazam! it works?

I red that the team is presently having problems with building having too much conditionning. Then, for recruitement geographic partitionning they did set up an 8 HR code wich actually is equivallent to an 8 bit number thus coding for 64 possibilities. The drawback of this system is that you have at least 8 conditions to add to your building only for it (plus any other conditions needed...).
To my opinion, it is possible to drastically reduce this number of conditions by changing the logic of the code (perhaps using a more thematic way), but this would quite certainly induce a slight increase in the number of different HR. That's why I wanted to know the max number of HR and if the "normal" ressources do count against that max (it seams not according what you said...). I will now think at it with all the needed informations...

5. Is it really necessary a Roman folder in the UI? UI means User Interface.
Actually this was quite a part of my question... lol
I know UI is only the interface, but other mods I saw did use a /ui/ROMAN dir, so I just wondered if it was normal and deliberated not to have one in EB, or a "still-to-do" part of the mod...

I really thank you guys for having answered my questions and even more for having doing it so quickly.