I highly suggest:

Stalin: Paradoxes of Power, 1878-1928

Stalin: Waiting for Hitler, 1929-1941

The author has spend the last 20 years in the newly opened archives and has gathered an incredible wealth of new ingratiation.

His books are about power, Russian power and Stalin power. There is lots of detail on all major foreign policy question of the Interwar period, it should be perfect for you.

A whole bunch, on vacation rn so don’t have good access to sources. When the Soviet Union Entered World Politics is a good history of the 20s, and Pariahs, Partners, Predators covers relations with Germany. Geoffrey Roberts has written a ton of journal articles and a book on late 1930s/40s Soviet foreign policy which you should try to read as much of as possible (http://www.geoffreyroberts.net/essays.php).

Not sure about your topics, but some areas of interest:

• How did the events of the Revolution influence early Soviet foreign policy? How did things change (And not change) with the end of the Civil War and the start of the NEP?

• How much did foreign policy events such as the 1923 German revolution and 1927 war scare influence Soviet foreign and, perhaps just as importantly, domestic policy.

• Did foreign events, both economic and polical, influence the Soviet political, social, and economic shifts which took place in the late 1920? How much or little?

• Did Stalin’s assumption of power see a fundamental shift in Soviet foreign policy?

• Were Soviet actions in Central Asia during the Revolution as well as China and Mongolia throughout this period colonialist/imperialist? Why or why not?

• How did the rise of Nazi Germany and the increase of tensions in Europe (Spanish Civil War, Anschluss, etc) change Soviet foreign policy? How did it influence domestic policy and society?

• Why did the Soviet Union shift from being Nazi Germany’s rival and committed opponent up until 1938 to a partner in 1939?