I'm w/speedy on this one. I ignored this one early in the game. If you don't do electrical enough to recall electrical 101 and are rusty or unknowledgable in regards to code then your better off not doing it. If these questions were for your own DIY project, I don't think things would have soured like they did. DIY'rs don't get paid but, if your going to charge for your labor, then you should be able to perform electrical 101 type tasks w/o having to ask DIY'rs to help you make that buck. Maybe if you send us a cut, we'd answer question for you all day long. These types of post will happen from time to time and if I don't agree with WHY something is being asked, I'll just ignore the post.
Q1: The voltage of the wires in a box has nothing to do with the fill capacity of the box. Put a box extension ring on the existing box (if possible) and you should be OK. NEC won't spell it out clear enough for non-eletricians to understand.