Not the bacon you were asking, I'm a

[fiery crypt]

thanks, Im just trying to blacklist certain items from being selected in the first place so im looking at that second half

since im doing PVE Conflict, would it be US_Campaign.conf ?

[hallow pagoda]

You can pick any of them, whatever seems closest to what you want for your faction. I just right click and select duplicate to... [your addon/scenario]. Name it whatever you want, and it'll save a copy to your addon's folder in the same folder structure. This will give you a good idea, even though it doesn't focus on entity catalogs, but those things are related to it.
https://community.bistudio.com/wiki/Arma_Reforger:Faction_Creation

This explains the entity catalog, but you'll want to know how to do the basic parts of the first link.
https://community.bistudio.com/wiki/Arma_Reforger:Entity_Catalog

Any arsenal will be populated by the faction's entity catalog, depending on what faction you set the arsenal to.

[olive crest]

Thanks bacon