Without going into spoilers too much

No npc followers/companions. The closest in game currently are wolves that once tamed can follow you around or be commanded to stay, and will attack hostile, but can't be taken with you on certain means of travels. (there are other animals that can be tamed but they can't be controlled in any manner nor follow you).

There currently is a very hostile sea monster and one other more passive sea monster. There are storms and high waves. There are plans for adding more content to the Oceans, but those are some ways off, likely a year away.