You can do both or either. Any information that you put on either of these wikis I'll copy over to the other. Thanks so much for offering to help, it's nice to see someone else as passionate about the game as I am.
This is something I need to discuss with people who are masters at formatting. Ideally I want some sort of infobox where you can click on various tabs and show how different government types/factions have different descriptions for their buildings, as opposed to just listing all the information on the page to make a long page, or (worst of all) creating multiple near-identical pages.
For now, yes. Please add the information and pictures for the different factions/government types to the pages. We will properly integrate the information later.
I would appreciate it dearly if you could contact me, as I need your help now more than ever. My email is email@example.com. If you could email me at this address, we can talk about the issue I have.
It will continue being a repository of knowledge for Empire: Total War. Pages will be updated here for ETW content before Total War wiki does, because I am sure that the information here will not be vandalized (I am not yet admin of Total War wiki if I ever will be at all and if I am not admin there there's no guarantee that the ETW content there won't be violated by people with authority). With your permission I would like to start carrying the building pages over to Total War wiki (after all, you wrote many of them); the quality of the work for ETW pages will be more paramount here but I'll strive to make sure they're of similar quality in TW wiki.