I can't speak about the population as a whole, but there was two groups of Jews who suffered a particularly cruel crisis of identity:

The first were those who had fought for and been decorated by Germany in the First World War. Jew's volunteered in greater per capita numbers than Germans in that conflict. These men and their families obviously aspired to be valuable parts of Germany, and to overcome prejudice and bigotry through hard work and sacrifice: their answer to the old charge that Jews weren't loyal to Germany was to point at their wounds and their Iron Crosses. The TL;DR is that many felt horribly conflicted, trying to balance a love for Germany with a horror at what it had become.

One of the most important - to historians - of such men was Victor Klemperer, whose account of survival and hiding in Nazi Germany has formed the spine of many historians' treatments of the German Jewish experience in WWII: http://en.wikipedia.org/wiki/Victor_Klemperer

The second were those who were married to Germans and whose "resettlement" was thus deferred by the planners of the Wannsee Conference. Many felt a deep attachment to both communities; the Protestant German writer Jochen Klepper, whose wife and daughter were Jewish, wrote that they "could not" wish Germany's destruction out of hatred for the Nazis.

So how did these Jews respond? Very often, with suicide, a way of of letting themselves die with dignity. Jochen Klepper's family, for instance, after failing to obtain permission to emigrate, committed suicide together. Many war veterans put on their old uniforms and medals before the act. Evans writes that by 1941, half of all suicides in Berlin were Jews.

Sauce: The Third Reich at War, Evans, pg 272-3

By all accounts, strongly. I assume you mean "just up to the Nazi era". I'll give two numerical examples, because it's easier to asses that way. First, German Jews served heavily in World War I (the common numbers you see cited are 100,000 German-Jewish soldiers, 12,000 war dead--these figures are only for Germany, not Austro-Hungary). This was widely seen as an opportunity to prove their loyalty to the Reich and prove that they, too, are good Germans. Likely in part because, unlike most European countries, there was already religious diversity in the national identity (i.e. Catholic Germans and Protestant Germans), it was easier for Jews to slip in as good national citizens who were Jewish, rather than merely loyal Jewish subjects of the empire, who were nonetheless not part of the nation-state. Jews struggled with this more in Poland and Soviet Russia/Ukraine/Belarus, where it was heavily debated whether they were part of the nation or part of a separate national group (the Soviet Union went with "separate national group", Poland it was a little less clear but leaned toward "separate national group").

Secondly, starting in the 20th century, German Jews also increasingly married with non-Jewish Germans. This steadily increased until for every 100 homogenous marriages between two German Jews, there were 59 mixed marriages in 1929 (which means almost a quarter of new marriages by Jews were out-marriage). There was a brief and even higher spike during the war years. This also varied between regions. In Saxony in 1926-9, there were 82.6 mixed marriages for every 100 homogenous Jewish marriages. In Prussia, it was 56.0 and Wuerttemberg it was 61.7, though the ratio in Baden and Bavaria was in the 30's, and even lower in Hesse. See this article for more. In the USSR in 1926, for comparison, the ratio of in-marriages to out-marriages was 100 to 18.5--lower than the lowest German region. Within the Soviet regions, Belorussia and Ukraine were much lower, but in Russia proper, by 1926 the ratio was 100:53.2, but this was the result of a rapid rise. Even in 1924, in Russia proper, it was 100:30.8 and in 1925 100:36.1. In Switzerland in 1930, the ratio was 100:19.0. I haven't looked at exactly when the U.S. reached this level of Jewish out marriage but I think it wasn't until several decades later--I believe after 1970. The comparisons are a little difficult, because 1) this data is based on couples, but U.S. data is generally based on individuals, and 2) this data is based on new marriages, and the U.S. data is generally based on population. In 1990, 50% of new marriages were out-marriages and higher today (58%). The best data on the corresponding rate before 1970 is 17% (this has an unclear start date, so let's say it covers the whole period about 1945-1970), which was 35% in the 1970's. But it seems like the intermarriage of the US in the 1960's was very, very roughy similar to pre-Nazi German in the 1920's. That should give you some sense of social integration.

It's generally said that pre-Nazi German Jews were one of the most, if not the most, integrated in Europe. They generally thought of themselves as both German and Jewish. On a personal note, my grandparents were German-speaking Jews (my father was born in Posen/Poznan when it was part of West Prussia, moved to Berlin when he was 12, and strong). The preponderance of their social network in New York was emigre German-speaking Jews. They met through the classifieds section of a German-Jewish newspaper (neither was religious). The "German" part of their identity even stuck with them in the New World, though they had no interest in "going back" after the War (they both left in the late 1930's). From what I can tell, this is quite a bit different from first generation Hungarian* or Russian or Polish Jews, who first of all were more likely to speak Yiddish so engage with Yiddish-speaking American society and two had a strong connection to a trans-national "Yiddishkeit" than a local national identity, likely as a result of nation-states forming relatively late in this region. This sense is more impressionistic than statistical. There were also more Jews, which allowed for distinctive Jewish politics and parties that were impossible in Germany. While Jews are associated with Communist politics across Central and Eastern Europe, they only seem to be disproportionately overrepresented in Communist leadership but less likely than average to actually vote Communist, at least in interwar Poland (Belorussians were the ones most likely to vote Communist). See Kopstein and Wittenberg, "Who Voted Communist? Reconsidering the Social Bases of Radicalism in Interwar Poland", Slavic Review, 2003.

* Many "Hungarian Jews", "Czech Jews", and others in the Austro-Hungarian Empire were also German speaking in this period, and thought of themselves primarily as "German". My great aunt grew up in Budapest and Vienna and spoke both Hungarian and German as native languages, but to my knowledge, in America, only ever engaged in German and French social networks, never Hungarian (this might partially be a class thing). Kafka, too, is considered a great German writer, but was a German-speaking Jew from Prague (he eventually flirted with a sort of Zionism, even studying Hebrew, but still likely thought of himself as both German and Jewish, or, perhaps more accurately, as a German-speaking Jew).