Sorry if this has been posted before, search pulled up nothing for me.
I am not really qualified to answer the question but I found this article quite interesting. It offers some good background on Mein Kampf in the English-speaking world during the time period you mention http://www.bbc.co.uk/news/magazine-30697262 A bit of it is anecdotal but nonetheless insightful.
I'm not sure if this qualifies as a source good enough for this sub(I've read the rules and faq but I'm not sure if a anecdote of someone historical relevant is valid),but in Homage to Catalonia,George Orwell says that he owned a french copy of Mein Kampf while he was in Spain,he was a journalist and member of farleft organizations.
The question of Mein Kampf's circulation is relatively simple. Casper has done strong work on the subject in 'Mein Kampf': A Best Seller (http://www.jstor.org/stable/4465572). Total circulation reached 7 million, the vast majority of which was within Germany, where it was considered the definitive text of the era. Goering once claimed, "we national socialists know only one Holy Writ, and that is Adolf Hitler's Meon Kampf." That said, it was a horriblebook used primarily as a propaganda tool and its sales numbers are heavily "inflated" (in some sense) in that you were essentially required as a German citizen to purchase a new edition. Very few Nazi elite actually read it and total circulation outside Germany totaled around 240,000.
As to Nazi influence outside Germany more broadly, my unsophisticated assessment is that it was relatively mild. But you'll have to await a more sophisticated historian for that question, as I have a math test to study for.