Awesome idea!!
I really like the synergy with flooding, gives it finally some more use,
also, i think the cost of 5
is enough, if you use this as a hitter, Abyss crawler is better 6|6 for 4
And since the ability can only be used if you have 7 or more creatures out, then play the Kraken and flood him, i don't think you have to calculate that through in the costs.
Based on my own superduperknowlegde of cards, flooding is absorbing a water quanta as well, so the cost for the ability would be 2
respectively, + a one time cost of 2
(inunduation) and the kraken cost (5), so it seems right to me.