It seems there are a couple of ways to import Blender objects into Unity ...
I have found that it is much easier to split larger blend-files into smaller ones (create separate files for most of the objects in your scene).
The official documentation states that :
'Unity natively imports Blender files. This works under the hood by using the Blender FBX exporter, which was added to Blender in version 2.45. Unity currently imports : all nodes (position, rotation, scale, pivot points, & names), meshes (with vertices, polygons, triangles, UVs, & normals), bones, skinned meshes, & animations.'
Just remember : you need Blender 2.60 or later !!! (In some earlier versions the FBX export is broken.)
Also : textures & diffuse color are not assigned automatically !!! You need to manually assign them by dragging the texture onto the mesh in the Scene View in Unity.
Q : Why am I only seeing half of my imported object ???
I made sure to set the normals to 'double sided' in Blender ... But still : I can only see 1 side ???
A : The answer can be found here :
If you want a 2-sided version of one of the built-in shaders which isn't currently 2-sided, you need to :