Multiple batteries, handlebar mount, (depending where you mount on the boat, maybe the floaty backdoor in case it decides to take a dip). I've been using iMovie on my Mac, but with any video software, there is gunna be a steep learning curve to begin. Even though I have three batteries and a charger on board, I still use the 720p setting with 30fps I believe.
With any kind of HD video, it's gunna take up space. Lotsa space. IIRC, each file will be about 4gb per full length video (on my setting. May also due to the format it is recorded in). If you plan on recording all weekend, a single 32gb card will be tight. With the prices of class 6 or 10 SD cards, there's no reason to not have multiple cards available.
On a side not about the battery, I found that after a few FULL cycles, the battery did last a bit longer.