Much, but why use such a big boat? Several smaller whale boats would be much more useful than that... monstrosity
As for bigger guns... Yes you get more firepower, but you get less rate of fire, much smaller ammunition stowage... Anyway, it's allready looking much better.
My next suggestion would be to get at least one of your directors as high as possible, such as above your bridge. More height makes it better for targeting.
I'll say it one last time. Your casements are going to be damnably uncomfortable to fight, and the lower ones are going to have issues in bad weather. But its not a huge deal if you must have them.