FPS model/animation setup questions

I plan on developing a "Halo" style weapon system I'm more of a programmer with a general understanding of modeling and animation in Blender. First I was wondering if I should have both player arms as separate models and animate them separately since they can equip different items and use them independent of each other, but there's the issue of what if during a reload animation both arms are required for the animation, so how do you animate that if they're separate models? Second question is if I should include all weapons in each arm model(.fbx) file, and animate them accordingly, while hiding the rest during gameplay in unity, or should the weapon models be separate from the arms models, in which case I understand I can attach the weapon objects to an arm bone in Unity, but how do you go about animating them if they're separate models? Generally how do I animate things together if each model is separate?