I made a UE4 theme for Blender (WIP). Get it here: https://gist.github.com/cyaoeu/ce1777866852268113bbab421c0672d8
Download the Raw file, then install it from Blender using Install Theme… in the Themes tab of the User Preferences. To make the fonts nicer you can go to System, then in the lower right choose Roboto-Regular (from /Windows/Fonts) as the interface font. Note that this will break international language support (so for example Japanese won’t work). After that save the settings using the button in the lower left.
I also made a skybox thing for the world by rendering an ansel 360 degree photo of the UE4 skybox. You can get the .blend file here: http://pasteall.org/blend/index.php?id=48451
You can create a new blend, link to the file, get the NodeTree contents (DefaultMaterial and UE4Skybox). After that go into the nodes for the world (Shader - World in the node editor), add the UE4Skybox by doing Shift+A, Group and select UE4Skybox, after that connect the UE4Skybox to the Surface input. There’s also a UseSkybox lerp which at 1 is the skybox and at 0 is a gray color (like in the BP viewport view). The grid is a bit strong when at 0 so you might want to just disable the grid floor in Blender when using that.
For the UE4 grid default material material you can create a new mesh, then create a new material called M_DefaultMaterial. Select the object, then go to the node (Shader - Object) and add the DefaultMaterial group node using the same method as above. Also add a Principled BSDF node. Hook up the DefaultMaterial into the Principled BSDF node, then from that into the Surface input of the MaterialOutput node.
After that change the viewport shading to Material to see the material in the view. You can also change it to Texture to see a colored UV grid texture.
After that click the F in the material you created (so it doesn’t get deleted), delete the mesh, then do File - Save Startup File. Now when you create a new scene in Blender you’ve got the skybox and material ready for use.