In regards to karve beam width, I tried the 6m width and the ship sail beam caught into the uprights and twisted the ship.
So I will build my longship dock overall 12m wide with 8m for hull clearance. Have to modify the current frame accordingly or change it, depending if everything collapses.

Even in storms the side arms of the river area do not swell up, that is why I started building there. The 2 arms I am using have an angle of approx 55 degrees to each other, so connecting the 2 separate docks will be a challenge to end up looking decent.
Went out at the river mouth to see and destroy some lurking rocks which were manageable with the low of the swells and also put guide pylons into place. Almost drowned a couple of times though ;).

In regards to the campfires, I dug a hole, placed it in and filled one "raised stone ground" back in, aiming at the side of the dug hole. It works with one refill, more than that ended up destroying the campfire and the stones popped back up. Now I am placing them on top of higher rocks or a short stone column. Have 2 resident one star deer in the area that I want to keep around.