Create your meshes + textures + skeletal meshes in 3ds -> export and import them -> create the materials -> create the level with the meshes.
You are much more flexible when you create the level in the UE4
what you are saying is i make the individual objects(custom doors,floor, pillars etc) in , export(.fbx)+import to UE4 and then create the level by putting all objects.
then compared to making the whole level in and then just running it in the engine.
I block my level out in unreal first using the brush actors, then convert those to models in unreal and name everything according to what im calling each model, then I will export those as models and bring them into 3d . Then I have all the scale information and basic blockouts done in one whack. Then I import them when finished into unreal with the same name I tagged them in the engine, and the actors are replaced with the new models.
Wow so you can export your basic bsp geometry to another program? Thats handy!
Ive been working in maya using a 1:1 scale with Unitys units and just snapping my basic shapes to the grid. I might try that other method though!