noob landscape question - how big is large?

When creating “large” landscapes for an open world in Unreal engine, it is recommended to use world composition/level streaming. If I want to make an open world game but the entire world would fit in a single, large landscape (8129 X 8129 vertices and 1024 X 1024 components or less) should I bother with world composition? Would the trade off of having more levels but several smaller terrains be worth it?

Depends on what you plan to do with the result.

If the landscape is part of a game you plan to sell then then being conservative with the memory footprint of the game resources is best practice.

The thing about UE4 though is design decisions can be included as part of the development process so while your doing the work you can decided at some point if you have to level stream or not.

I’m not the most qualified noob to answer this question, but I’ll try give you a better view on the subject.

I’d use a single landscape actor, anything larger/detailed than these dimensions I’d use W/C
8129x8129 127 4 (2x2) 254x254 1024 (32x32)
1009x1009 63 1 63x63 256 (16x16)

But it all depends on your target platform and project type, are you trying to create a detailed game scene with many assets or a landscape visualization with instanced/procedural foliage and few Mesh Assets, are you going to be the only one viewing the scene, are you gonna render out in matinee.

I can get away with a 4065x4065 127 1 127x127 1,024 for landscape visualization with about 60-90 fps with instanced grass and procedural foliage (i5 4690k GTX970), no optimization.

tl;dr no one can really tell you, it all comes down to the project scope and your target hardware, after a while I’d assume you’d get an idea on landscape sizes for a project