I've gone there the last two years. You probably want to get there a couple hours early (if you have the time) to get a decent view. There will be a seating area for VIPs in the front, and it's SRO for everyone else. If you get there early, you can also see most of the performers rehearse, so really you'll see most of the performances twice.
It is 100% free. The performers are entering from another area, so while it's not impossible to meet them; there's not an organized opportunity for that.