OK, I think you need to read up quite a lot on the whole UV-mapping thing 
You wrote: “deleted everything from the uv map except the top face” - this means you have an imported mesh with areas not UV-wrapped = not good
UE4 works with (can work with) several UV maps on a mesh, also for proper light handling. If you want to make anything remotely serious, you have to have a profound understanding of how this works.
There’s a trillion tons of info about UV mapping out there, Blender is a fantastic application to handle this, and you cannot / should not be able to do any unwrapping inside Unreal, that would not make a lot of sense IMO.
Perhaps you’d want to use Unity instead, it is somewhat simpler in this whole regard (Unreal is a better tool, but it is therefore also more demanding of the developer)
Also, it would not make any sense to unwrap Unreals internal (‘native’) static mesh, it’s not there to show anything finalized, you’d need to use a 3D application for this.
Perhaps read into Unreals BSP’s, but in general it sounds to me that you are trying to invent a technical solution to a challenge and that there would be a much simpler way to do it and that you should probably ask how to make that game instead, and start there - or start by ‘just learning’.
Think of that person trying to build a robot to change the tires of his car asking how to program the AI on the robot… when he would probably be better off learn how to fix cars from ground up instead 
Cheers!