So my wife is going to come along to just hang out with me away from the convention.  Food trucks, meals, bars etc.  She is not a badge holder and is not attending the convention proper.  Should I add her to reservation before hotel info transfers or just deal directly with the hotel later before we head down or just even at check-in?  

It probably doesn't matter. Why not do it now?

Just wasn’t sure if her not having a badge would
be problematic having her listed as a guest on the site.  That’s all.  Just being overly cautious to not screw up a downtown room.

Nope, not an issue.