Generate level from an external file

I am new to UE but not to coding, been reading through UE documentation and got very confused of what is possible and what not with UE, Slate, etc.
I am planning a standalone windows application that should generate a 3d level based on a imported 2d map file. Essentially I need:

  1. GUI with a windows file-picker and a
    couple of radio-buttons
  2. 3d viewport for reviewing the results of the import and
    export-as-FBX/OBJ function
  3. enhancing of the model: adding lighting and materials (again,
    should happen in code without any
  4. finally a full-screen 3d fly-through of the level

The app should run standalone and shouldn’t involve any interaction with the UE Editor, everything should happen in the c++ code.

I’d be glad if friendly community could point me to the right components of the engine, which would enable me doing it. Especially my current findings are, that doing GUI in unrealEngine

Hi … did you find any solution for this, we have exact same situation which we need to load external level into unreal application thou.