Your invitation says how many seats I have reserved for you, I would prefer you invite as many as I have planned for.
Wear whatever makes you feel comfortable. Dresses, suits, jeans, tee shirts.
I would prefer you invite only one extra guest, as we have limited seating. However, if you're wanting to attend and can't get anyone to watch your kids, I totally understand. We will accommodate if necessary. I want everyone to have the chance to come :)