I am especially interested in the subjects:
Thanks!
Stalin's mental state, modus-operandi and the overall Soviet Union strategy mentality
Earl K. Ziemke - The Red Army 1918-1945: from vanguard of world revolution to US ally is compact and comprehensive about soviet military activity throughout the world war. Another, somewhat more expansive source is David M. Glantz's When titans clashed: how the red army stopped Hitler. Both are good for addressing soviet strategy and military capability during WW2.
As for Stalin personally, I recommend his biographies, especially Simon Montefiore's Court of the red tsar. It goes into as much detail as is available about Stalin and his circle at any given time, including the world war. It, however, doesn't put exclusive focus on the war or Stalin's attitude towards it, so other sources may be better.
Hope this helps.