You will need to "check-in" at the lobby first. The CM will escort you to the elevator and use a special key to enable to elevator to go to the lounge. One night we met her as we were getting out of the elevator so she just told us to get back in and used the key then.
And yes you can hear the music - it is played inside the lounge and also on the balcony. If you are paying close attention you can actually see Tinkerbell "fly to the castle". I missed it the first night we were up there.
The balcony wall is HIGH so no worry about falling. But if you have little ones you may want to hold them.
Enjoy!!! If you have little ones the BEST thing about watching them is that when the show is over you can usher them right down to the room and put them to bed. NO fighting with the crowds.