Tiled Landscape and Wold Composition + Rebasing


I would like to ask a few questions about MP and large worlds in UE4. Our team working on a game and we would like to make a map about 12x12km2 of size with Tiled Landscape and streaming option. I made a few test how the streaming work with dedicated server on and it seems that it mostly work OK. but my questions:

  1. does world origin rebasing works in MP (could you please exactly explain what is it doing)
  2. how to place static meshes on this kind of tiled landscape ? (problem is when i put some static mesh it simple spawn elsewhere outside of the map, so no sure how to manage it to work)
  3. What is reasonable map size for MP game without tiled streamed landscape ?
  4. how to make sure that character spawn on correct location, when he logged out from server and then back once i save his transform(pretty confusing) ?

I know it could be pretty basic but we would like to make it right and dont develop own server-client system.

Thank you for any help.