The ability that defines Necrogoyf's power works in all zones, not just the battlefield. If Necrogoyf is in a graveyard, that ability will count itself.

If Mystic Redaction's last ability triggers during the cleanup step because you are discarding due to maximum hand size, players will be able to respond to that ability. Then, when all players have passed priority in succession with the stack empty, a new cleanup step will occur.