I'm probably a little late to answer this but ah well.
Firstly, the map will always be one big object. Because the importer does not import brushes but draw surfaces. You would have to manually seperate everything in Blender if you wanted to start modifying it. Which to be fair, is not too hard.
Now, your first question is a little confusing so I'll assume what your saying is... You can import into Blender fine and the textures show in Blender fine but when you export as fbx or .obj and then load it into Unreal there are no textures correct? If so its because the .fbx will not store the textures so you would need to manually assign the textures in either Unreal or Blender I believe. I think if you do it in Blender you want to make sure they point to your Unreal Project Folder.
You also said that the scale was not right. Well, your gonna need to work out the conversion yourself to match the scaling issue because your porting from one engine to another.
But I'm presuming your using the blender bsp import tool and stuff so I could be wrong.
It's doable for sure though. (What your trying to achieve) just time consuming.
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Port bsp to any format what the UE can see
in General Modding Discussions
Posted
Thanks, I will keep that thing in my mind.