How to determine polygon budget strategy?

I'm wondering what you think is the best strategy when building & importing models.

Let's say I have a large scene, but it's constructed just of boxes (from Blender). Let's assume all use the same material, no texture. Now, what are the considerations for how this thing is made:

a) if I use individual boxes for each part (separate meshes), the file size will be big. b) if I use references to one box mesh, the file size will be smaller, all parts will just be transforms really.

Are there any performance improvements with either? I imagine it would very much depend on the platform. Let's say iPhone.

Any tips for exporting from Blender regarding it making copies vs references? I'm not convinced that my 'duplicate linked' objects are saving me anything at all by the time they get into Unity.

Having all the boxes as one mesh is far better, especially when working with the iPhone, as it reduces the number of draw calls dramatically. If you need the boxes to act dynamically, you can even give each box in the mesh a bone, and they will act like they are separate, although they aren't.

You don't have to write a custom export/importer to import 1000 boxes in a mesh. Instead, just make all 1000 boxes, import them into Unity, and use Mesh.CombineMeshes to finish off the job. Have a look at this post and this one on the subject. It seems to be quite a popular topic.