What is the ruling on a man growing his hair long? Is it from the Sunnah? And did Umar ibn al-Khattab, may Allah be pleased with him, have curled mustaches?

Lengthening the hair for a man is from the customs of habit, not from the devotional Sunnah. As for twirling the mustache, it was reported that Umar ibn al-Khattab (may Allah be pleased with him) used to twirl his mustache when a matter distressed him or he became angry.