Hi,
It depends on your project, if most of the time all landscape surface will be visible, there is no need to cut it to sectors. Usually for big worlds it’s better to subdivide landscape to tiles, so you can stream in/out distant parts of it. There is a tool that helps you import tiled landscape. Community made a nice tutorial about it here: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
Tiled landscape will still work as one seamless surface in the editor. Another benefit of subdividing your world to tiles is that in the editor you can load only part of the world and work on it. Big worlds with a lot of content require more machine resources. You want to keep your working set as small as possible to have responsive editor.
Landscape (heightmaps/weightmaps) texture streaming works automatically, you don’t need to think about it. It uses same streaming mechanism as all other textures (based on distance from camera).
All worlds that fit into world bounds (20x20km) should not use origin rebasing. I will disable it by default in next release, as most of the projects will now fit into new world bounds.