(Sorry, my english is not good   :-/  )

In my opinion (for FSX's constraints):

1- The full passenger cabin [(without animations) or (a few animation)]  + full virtual cockpit  is the right choice  

2- Less polygon model for virtual passenger cabin : The reality view in the virtual cabin should be provided with the photoreal textures  

For example : The best choice for virtual passenger cabin  same as CS 767  :)