Does it matter if the size is 1m or 1cm in ue4? In blender its 0.5x1x1m big. And it’s the same size in ue4.
Does this bring problems with lightmass, dynamic light and so on?
As you can see the lighting works. Every single cube of these 4 has lightmap resolution of 128. It looks normal or?
Oh and, how can i make the 4k texture on the ground even sharper? 
It’s not sharp enough for close views.
It could ‘matter’ if the actual size of the object is going to be 1 cm in the scene / level. What import settings did the mesh have? There’s a ‘Convert to UE’ and a ‘Keep Blender space’ in Unreal. In Blender, there’s also changing the scale in the export settings from meters to centimeters. Does it function correctly? That’s another question.
what you mean with actual size is 1cm in ue4? in the image its in meters, not cm. i didnt change the size. its original size from blender. why would i convert it to ue? that is not required i think
It probably got converted to UE space somehow by ‘default’ during import. Blender space is 1 meter is 1 Blender Unit, and UE is 1 cm per 1 Unreal Unit. The lighting does get various issues or challenges / limitations to contend with at larger and smaller scales, such as a player that’s 1.8 m tall but looks like they’re 1.8 cm or so tall. Yet it depends on the textures, UVs, and settings for things for it to maintain quality and accuracy, I think. To sharpen the floor, open the texture in the texture editor (from the Content Browser, or in the material double-click the texture preview image), and scroll down to Filter. There’s a bunch of different levels of Sharpen to apply. Another approach is use an image editor to sharpen / blur the texture before importing to UE, and perhaps trying one of the Sharpen levels under Filter. If the texture file is 2K or 4K, it may look better too.