newbie blender pipeline question

I'm just starting to learn Blender, I'm working on an iOS app involving a digger and I want to create a low poly digger in Blender. Up til now I built the digger in Unity using cubes and empty GO's for the pivots. Now I want to have a proper skinned model. I have a few questions that will hopefully set me on the right path. Apologies if this is covered elsewhere, I did look and found nothing specific to my needs...

I want the meshes to be: (1) the Chassis & Tracks; (2) the rotating base, cab, engine etc; (3) the upper arm; (4) the lower arm; (5) the bucket. I'm animating them in code. Should I make 5 different Blender files and import them as different Transforms? Or should I have 5 different Objects in Blender, parented to each other? Will bones help me, since it's an inorganic object which shouldn't deform? Can I manipulate individual bones in code in Unity, as if it was a child Transform?

Thanks for any advice!

For a low-poly animated object, bones are the way to go, because you won't be using a bunch of draw calls then. You'll have to do some scripting, probably based on naming, to get references to them, but you can work with them like any other Transform.

http://docs.unity3d.ru/ScriptReference/SkinnedMeshRenderer-bones.html