I think I have the structural skeleton for TIWTBWO #1 fixed.
These are fiercely political books. (In the sense of having complex and involved internal politics, rather than mapping simply or directly onto any real-world political divides.) I have come up with the matrix of six axes their diplomats use to assess the political position of newly contacted worlds, and I see where in the story an example relevant to each axis of variation fits, so that gives me a structure. (My protagonist, fwiw, comes from the perspective that that model makes for pretty graphics in the reports you have to hand in after making contact but is of little practical use with the immediate details of any given situation. And I very much intend information about the political axioms and assumptions of the wider setting to come across to the reader in what sorts of variation those six axes don't cover.)