This summary is drawn from the Rebbe's letters to him (about 5710–5717, 1950–1957); I did not find a published biography.
Chassidic ways. The Rebbe noted the custom among Anash not to report when things are peaceful, and encouraged him to write good news as well (IK 2069). He taught to reflect on past requests with gratitude, recognizing G-d's kindness (IK 2339), and that Kislev is a time of miracles, spiritual and physical (IK 3950).
Sacred trusts. Sacred tasks should be entrusted only to reliable people, and precious items safeguarded (IK 2669).
History and sources. The Rebbe corrected an error in a citation about the Previous Rebbe's view of the Vilna Gaon, tracing it to its source (IK 4703). On a change of residence, he wrote that it can bring new mazal, and that true unity is needed in material and spiritual life alike (IK 2537).
Sources: the Rebbe's letters cited above.