If this card turns out to be good it will absolutely turn out the be tier 1.
The hero power won't likely see completion unless the deck is specifically geared toward it, but it is fantastic for control decks who don't want to run the dude or murloc package as just a plain token. Having a 2/2 every turn that the player HAS to deal with is incredibly powerful.
Seems like each Horsemen will probably have some kind of added ability just like the totems as the Hero power to "ALL four", not just four copies.
Probably not. Check the 4 Horsemen Token minions - none of them have any "minion signs" (like thunderbolt for continous effects, heart for lifesteal), so high chance they do not have an added ability. Though I could be wrong, this is speculation based on observation.