This summary is drawn from the Rebbe's letters to him (about 5713–5722, 1953–1962); I did not find a published biography.
Strengthening others. The Rebbe thanked him for strengthening Yiddishkeit and for helping others, spiritually and materially, and wrote that such help brings multiplied blessing from G-d (IK 3985). Seeing tangible results from inspiring others, he wrote, is a rare blessing and a sign of worthy effort (IK 2354). He thanked him for his efforts to find a doctor for Kfar Chabad, teaching that every sincere effort in holy matters has value even when results are not immediate (IK 5050).
Chabad books. He guided him on which Chabad books to acquire first for a library (IK 7000), on publishing chassidic discourses for youth in language suited to them while preserving their content (IK 6980), and encouraged sharing inspiring memories and printing Chabad articles (IK 7559).
Faith and Ahavas Yisrael. The Rebbe wrote to him that what we accept today with faith may become clear to the intellect as we grow (IK 2649), and urged Ahavas Yisrael in daily life, since blessing others brings G-d's blessing in return (IK 8404).
Sources: the Rebbe's letters cited above.