you need another brood box before you add a honey super. you can put both on, but no excluder until they are working the honey super. you may want to skip the excluder all together. do it now, or they will swarm.
addition: when you add the next box, take some of the frames of brood from below and put in the new box. take them from the center and replace with the new frames of foundation/drawn comb/starter strips. most of the time, you would not want to break up the brood nest, but since yours is all brood, you have no choice. put the frames that you pull into the new box, in the center. with any luck, the queen will take advantage of the empty space in the middle and work her way up.
you may also choose to put the new box under, but that's a lot of work when the hive gets that big.