This summary is drawn from the Rebbe's letters to him (about 5721–5723, 1961–1963), which show him serving as a congregational rabbi; I did not find a published biography.
The mechitzah and shul standards. The Rebbe wrote that accepting a rabbinic position requires ensuring proper halachic standards, such as the mechitzah (IK 8802); analyzed halachic sources on synagogue layout (IK 8828); stressed that upholding standards like a proper mechitzah is essential (IK 8875_star); and wrote unequivocally that playing bingo in a synagogue is forbidden (IK 8941_star).
Halachic questions. Arranging a proper sale of chametz remains beneficial even where some might take from it (IK 7248), and he clarified the calculation of the molad and its bearing on setting times such as weddings (IK 8795).
Sources: the Rebbe's letters cited above.