Enjoy the movie!
So, regarding eugenics: the book "The Coming of the Third Reich" by Richard J Evans delves a lot into Imperial German and Weimar politics, as you might expect for a book that ends in 1933, and while I feel like a bit of a douche for adding yet another name to your growing pile of research material, I think it will hold a lot of information on domestic aspects that you might need, and that would still be relevant to an alternate Germany. On the subject of eugenics, the beginning of the push in Germany came, as in Scandinavia, from the medical profession, with considerable assistance from the bureaucracy devoted to welfare and the Social Democrats and other parties in government.
With Weimar's extensive welfare, as well as the spirit of scientific excitement in Germany during the time, there was a vigorous effort to turn welfare allocation into a science, and doctors were the prime instigators of this quest, firm in the belief that they could create a genetically healthy population and thus boost the effectiveness of both their practices and welfare programmes. As you can quickly surmise, Weimar's tremendous financial woes added a grim urgency to the endeavour - they were, in their own mind, trying to save the welfare system by pushing for harder and harder stances on eugenics.
ITTL the welfare state is unlikely to be as large as Weimar's, the government is unlikely to house a large SPD presence and the financial woes won't likely be there, or not on that scale, so you might well be looking at a development more similar to that we saw in Scandinavia, Switzerland and the United States.
BTW, Britain kind of backed itself into a corner there, I agree. They will likely push for officer control of any Dominions Navy anyway, but who's eager to go serve and die under British officers again after Gallipoli or what happened to the Canadians in operation Georg?
EDIT forgot to answer about an Anglo/German naval agreement. I don't think Germany would have accepted anything less than parity before 1914. Now, however, the situation is somewhat different:
1) Wilhelm has been somewhat sidelined, although the new framework for chancellor appointments sort of brings him back in the loop to an extent.
2) OHL and the government have a wholly different and more moderate attitude, further tempered by the experience of the war.
3) With the development of powered flight, which was combat tested extensively in 1919, Germany might see a chance to win a diplomatic victory with reasonable but limited naval concessions, and still compensate in military terms by investing heavily in naval aviation.
This makes a lot of sense for Germany in Europe because of the nature of its coasts and where it needs to operate. They still need the High Seas Fleet for power projection, naturally, but as of now their colonial empire is kind of strange, and their Chinese concession is very isolated. The Germans must know that even with a big high seas fleet, the Chinese concession is hard to defend without basing rights elsewhere (where do you house a gargantuan HSF as opposed to a merely large one?); and that while the experience of the blockade hammered home just how important a strong fleet is, the High Seas Fleet was not enough to break it, and new thinking is required.
I don't know if there's any naval expert here that can give a better input than mine, that would be appreciated - I simply think that Germany would indeed care about its naval strength very much, and likely push for local parity in Europe, but also that the experience of the war taught them that they need to build a navy that suits their strategic needs, rather than Wilhelm's pride.
