This will so much add to the pleasure of naval combat. Possibility to defend against multiple ennemy ships, and all the strategies already mentionned, with the liberty of the crew composition, it sounds really good!
I hope there's some "camera follow ship" functionality, otherwise I imagine it could be problematic to select and give orders to units. "This guy, I'll send him to the deck where he'll be more useful... Oops, missed it... Come on, I'll catch you dude.. hey not here you fool!! Man overboard!"
Will the spell casters be of any use aboard ?