The ssue is space inside the hull. There is no room for anything more than a stanard 6 cell pack unless you start cutting into the hull. Even then, I think it would likely be forced to build some odd custom pack just for this one boat. Seems like too much effort, particularly if you are even remotely considering lipo. Just go lipo if 6 cells isn't enough for you.

I'm new to boats, so I can't suggest anything in terms of motors just yet. I've asked questions of this group along the same lines. In my case where I just want to use the stock prop for now, they suggested a couple of high torque long can 550 motors. Not too low turn.

Yes, water does get into the hull. I suspect most comes from splashing by the transom.