I've probably played about 16 hours by now. Fully upgraded my ship as much as I can and I've started looking for the elite plans, but I haven't even got far enough in the story to be able to dive yet, so I can't find most stuff. I've taken over about half of the forts around the map and I've killed a bunch of animals and upgraded some of Edward's equipment. I've tried fighting 2 of the Legendary Ships and I couldn't defeat either of them, although I can take down any ordinary ship including up to level 60 Man o' Wars. I've got my fleet fitted out with almost all Man o' Wars, but I don't really see the point in it now and the monetary rewards aren't high enough to keep bothering with it.
I guess I'll do the rest of the forts and then crack on with the story. I still dislike the on-foot staff and while I really enjoy the ship battles, boarding and taking over enemy ships gets very tiresome (especially when it glitches out, which is pretty often). I think I've just finished chapter 5.