The overload stuff is mostly to win back the board if you get behind against an other agro deck early. I think that this deck will be better in the late game as eralier murloc decks cause you can easily refill te board with ghostlight angler, underbelly angler and scargle. And when you build such a board you play soul of the murloc so you will probably have a lot of minions on the board to use bloodlust on next turn.

Or do you get coppies of you battle cry minions on the board?

If i understand this correctly this is why its good with shudderwock: If you play this with shudderwock in hand you will get an extra copy of shudderwock. And when you play shuderwock it will repeat the battle cry of this minion. So cause you still have another shuderwock in your hand when you play this you will get shuderwock again so you will have infinte shudderwocks. You cant play 10 shudderwocks the same turn like in the old shudderwock days but you can play one evry turn and if you have played some good battle cry minions this infinte value could be used to win you the game.