Hello,
so basically I THINK I have too many actors.
As you can see from the picture a house that I’ve built consist from ~70 actors(static meshes), and I have like ten of these kind of houses. So does it really matter? A simple example: will my “Lightning building” speed increase if I somehow reduce the amount but not the size of them (Basically if I SOMEHOW group/recreate some static meshes into one big and therefore there’ll be less actors).
Thanks and sorry for grammar, not so good at it.
Each object will increase the draw calls which has a significant performance impact in the final product–if you’re concerned about real-time performance then it’s good to keep the number of objects low if you can. If you have very simple objects then it’s best to combine them into a single object, you can start by attaching objects that use the same material. You can also use Blueprints to place and position individual objects and it will automatically combine them so that they reduce draw calls: Instanced Static Mesh | Unreal Engine Documentation
In certain situations, reducing the number of objects can slow down building lighting–this is due to how Lightmass works in that only one thread can render an object at a time, so if you have a large complex object then only one thread will render the lighting and it’s possible that other threads are finished and waiting for the last object to finish without being able to help.
On the other hand, this avoids possible problems with lighting “seams” in indirect lighting due to overmodularization 
Understanding culling is critically important:
http://timhobsonue4.snappages.com/culling-visibilityculling.htm
For example, you could have a map with a large number of static meshes but only a few are rendered.
The solution is hierarchical instanced static meshes with culling. If you repeat a mesh HISM makes many objects behave as one. I have 400,000+ meshes all with lighting, collisions and lod in one level. Culling really far objects helps depending on mapsize.
More draw calls can slow down performance. Draw calls are subject to the amount of polygons shown on screen.
For backgrounds make sure to use the LEAST amount of polygon meshes possible, i.e simple boxes with texture normal to give that bump effect.
