I did not find a reliable published biography of Reb Alexander Sender Yudasin; this summary is drawn from the Rebbe's letters to him (about 5715–5722, 1955–1962).
Visiting settlements and awakening Jewish hearts. The central theme of the letters is outreach to towns, kibbutzim and settlements in Eretz Yisrael. The Rebbe wrote that leaders of Anash must not let comfort or the absence of opposition weaken their commitment to visiting and uplifting Jewish settlements (IK 4011), and that every Jew's heart is receptive to Torah and mitzvos when approached with inspiration (IK 4238, 6557). He urged him to influence his surroundings in every possible way, without waiting for ideal conditions (IK 3755), and to keep increasing Torah study and outreach without fear of obstacles or opposition (IK 5046).
A mikveh in a kibbutz. On building a mikveh in a kibbutz, the Rebbe wrote that while peace is paramount, it should not delay important actions (IK 4348).
Spreading Chassidus. The Rebbe stressed that spreading Chassidus transforms both individuals and the world (IK 4924), encouraged parents to inspire their children to spread Chassidus wherever they are (IK 7981), and urged establishing a "chazakah" in Tanya study, especially in Adar (IK 8361). He expressed surprise at not receiving reports after Tishrei, and urged him to expand his activity after Tishrei in both quantity and quality (IK 3860), and not to miss opportunities for positive influence, including at a gathering of rabbonim (IK 4158).
Halachic questions. On determining the yahrzeit and Kaddish when a passing occurred in another place or time zone, see IK 4667; on caution in publicizing Sefer Torah corrections, see IK 5046.
Sources: the Rebbe's letters cited above.