The pics released show what looks like a forum, so I'm guessing that's the first building. I'm guessing it's either the first building for everyone regardless of government type or it's the building exclusive to Classical Republic. I too would like to see a choice between mutually exclusive buildings for every district. Your proposal for an observatory is an interesting one. Choosing between that for a bit more science and a university for the housing could work. I'm not sure the Theater Square needs another building, though, since it already has a choice between two museums.