If it's not opening night, dress casual or business attire is ok.  I have seen some people attend in jeans.  I think it is more acceptable to wear jeans to a matinee.  I think people dress less and less as the theaters are a huge day trip event and people like to be comfortable.  I know my mother went on a group trip earlier this year and almost everyone was in jeans.

For a night show, I would wear black pants and a pretty top.  Definitely bring a sweater.  The theaters can be cool.

I can't help with the restaurant, but you can't go wrong with black!  If in doubt, a nice black dress or skirt would be fine.

Have a great trip.