And is there a timeline of events that makes this more apparent, or is it the sort of thing that's hard to pin down like that.
"Progressivism" in the title is mostly meant the way you would expect in an advanced undergraduate history course. Increased acceptance of marginalized communities (LGBT groups, racial minorities, new or previously rejected schools of thought/understanding, religious minorities, etc.) increased representation of those groups in media are what stick out to me more than a decade after learning about it.
The cultural push against it, from what I recall, involved a conservative coalition of religious groups, disenfranchised young men upset with the cultural shift they were seeing among their peers, and nationalists blaming these new ideas and developments for ruining the country, among other groups.
How well does my understanding fit in to the realities for pre-Nazi Germany? Obviously there were economic and political concerns impacting these groups, and it's impossible to divorce the two from social concerns, but is it generally fair to say
There was a progressive movement in the Weimar Republic, with a corresponding conservative counter-movement
Your understanding is correct. In the 20's Germany there was a bout of progressive tendencies.
Let's not forget that the Weimar republic was established by left wing, especially the SPD. The first elections were won by let's say progressive forces: liberals, social-democrats and Zentrum (at that time they defenders of the democratic republic) and the constitution is made by them(so social-democrats, liberals in European way and center right Christian democracy). In the election of 1919 they had a majority and the first nail in the coffin came quickly: the Versailles treaty that help to undermine this coalition.
Now for the cultural part. There were important changes in the era as you rightly mentioned. On one hand, some of them are a product of ideas before the war: women suffrage or equal pay became law after the war but it was advocated by socialists and some liberal before that. Conservatives did not like that.
On the other hand, the war and it's upheavals gave way to new ideas in fashion, art, music etc. Let's take some examples. Fashion( this is especially for women): shorter skirts, new hair styles, smoking were new and at that time for conservatives were scandalous. For art: the new art like Dadaism and expressionism(this one existed before) became popular and it represent the breaking up of old norms or traditions and were in a way a protest. Not by coincidence the Nazis painted it as "degenerate" art. Music: the new music was also shocking for the conservative establishment because of those crazy new dances, more sexualized dances and for the horror of some conservatives they were genres produced and sung by blacks. LGBT rights: now here it is difficult to portray it as increased acceptance. Homosexuality was still criminalized and a taboo, but you have Magnus Hirschfeld with his institute and the Nazis portrayed homosexuality as a communist thing. I do not think that played an important role in initiating the conservative backlash.
There were some aspects that you mentioned which I do not think that played an important role in this progressive movement. Religious minorities for example. If by that you meant Jews, I think that it is not the right category to put them. They were rather seen as a race and not exclusively as a religious group.
In closing, it is also important to understand that those new ideas did not swept Germany as a whole, but rather the middle and upper middle class in the cities and some parts of the youth in those cities. This is not necessarily enough to kick start a backlash of such proportions and thus other factors were at stake, as you mentioned. Scare of communism, the hatred towards the Versailles system, economic hardships, political instability also played a very important role. The cultural stuff was also crucial as it made more easily to paint an image of decadence.