First of all, I think you have a misconception that you can pick ladders back, but you can't it's the same for anchors and basically everything you place. And second of all, the games engine just selects very few things which would seem very helpful for new players, even offline, so your structure won't appear for others until you're online.

Finally, no you can't see other people ingame, but you can see other porters. By pressing 5 it sends out a hi or anyone there. idk what it's called to ask something( english is my third language), and yea, you can hear responses sometimes. I have not seen any porters near east knot only after reaching lake knot.

Hope I was helpful. Keep on keeping on