Get there early and bring your walking shoes. Last year we were late on Sunday and had to walk an unbelievable distance. And even if you are early, the hills and steps make for some strenuous walking.
I just learned last year (after like 50 shows there) that there's a free shuttle from the visitors center which brings you all the way to the top entrance. I like to walk the whole area, but it came in handy when I was running a bit late and knew the top entrance was going to be a less crowded getting in.
Yeah, you can pretty much fire up green in front of security and they won't bother you ... but they will ask you to not smoke cigs. Yet strangely enough, getting into the venue is more on the the rubber glove treatment end of the spectrum.