If I remember what my history teacher taught up, the first one, Quota Act of 1921 limited the quota to 3% of immigrants from the census in either 1900 or 1910 (my leaning is toward the latter). The follow up, 1924, set it to 2% of immigrants from the census in 1890. The major immigration boost and the flowering of the Progressive Era did not occur until after 1890, when people realized that "hey, the States are actually a good place to live, screw famine." This in effect slashed immigration numbers to a screeching halt. However, my history teacher seemed to put the two Acts in the context of mostly preventing Asian immigration, as opposed to immigration in general, which makes sense, when put next to the numerous legislation attempts to limit the integration of Asians in the Western US.
I believe that they should have been more than sufficient. However, with the outbreak of the Great Depression, there was a general alleviation of debts to a certain degree for all parties involved (though not completely). However, the rise of the German economy was too fast for it be "Hitler is just damn good at it," that something else, perhaps on a societal level, helped to push the economy forward. Even with a weak military, a strong economy is more than enough to produce a large army very quickly. I would attribute more toward the appeasement aspect of Europe that WWII actually began, and that the economy was also supported by the new revenue caused by appeasement, along with debt forgiveness.
Isolationist to the extreme, but never to the extent of most of the Eastern Asia countries. I can't remember the exact deal or concept name, but there seemed to be this policy of that each hemisphere would only deal with their hemisphere. US messed with South America, and half of the things in the Pacific Ocean (such as the Philippines), while Europe would deal with Europe, Africa, and Asia. A typical New World-Old World split. One could argue that it's not truly isolationism, but for the sake of history, American and European relations were less than open to the idea of "let's be friends." A begrudging acknowledgment of US sovereignty was not gained on the British side until 1812 and the Napoleonic Wars, at which point, Napoleon seemed to recognize the States on the same level as any other economy. We had what he wanted (the good old Yankee Dollar) and he had what we wanted (New Orleans).