This summary is drawn from the Rebbe's letters to him, mostly from the 1940s (with one from about 5720, 1960); I did not find a published biography.
Halachah and Chassidus. Much of the correspondence answers his questions: how "mikra kodesh" applies to both festivals and Shabbos (IK 229), proper pronunciation in certain prayers based on authoritative sources (IK 243), how emotions and intellect give rise to "letters" only at certain stages (IK 328), and practical details of tzitzis (IK 342). Clarifying the Torah, the Rebbe wrote, is rooted in the earlier authorities, not in personal innovation (IK 7804).
Supporting education. The Rebbe thanked him for facilitating a donation and encouraged using one's abilities for communal good (IK 372), and urged proactive fundraising, communal and individual, to support teachers (IK 460).
Sources: the Rebbe's letters cited above.