Is there a way to combine static mesh into a single mesh inside the editor like there was once in UE3/UDK This feature was super useful for completed levels as it severely reduced the amount of Mesh draw calls. Thanks Guys.

Check out Editor Preferences > Experimental > Actor Merging. If you enable that you can merge a blueprint(or multiple selected meshes in a level) into a single mesh, which also preserves the lightmap UV’s and turns them into an atlas UV.