In the campaign I tried to load my stack of doom, on a ship. Sovereign plus groups of archers, groups of hammer men, and some other solo units, including janusk. I was expecting something along the lines "not enough capacity for all units" But I tried cause I didn't know what the transport capacity was anyway cause that wasn't listed anywhere (that's also another issue)

To my amazement the stack moved in the water, but then it couldn't move anywhere else but back on land or beach. However on the same tile the ship was also present as a separate stack. I could move my troops by first moving the ship on another ocean tile and then moving my stack again on the ships new location. The weirdest part was that the move points of the two units seemed to be linked together in some very weird way.

Also I could abandon my stack in the middle of the ocean and it would be unable to move, since without a ship on a neighboring tile land units can't move into the ocean?

Also the first ship you get in the campaign has more essence than the sovereign ....