That's awesome, dude - I'm stoked for you. Your story of discovering Metallica an album at a time took me back to when I discovered them.
The show should be amazing. Slayer is fucking godlike live. Check out as much of their 80s output as you can before going too see them. My personal favorite album of theirs is Seasons in the Abyss, but all the albums before that absolutely kill as well.
On a tangential note about live shows, if you ever get the slightest inkling of a possibility of a chance to see Iron Maiden live before they retire, DO WHATEVER THE FUCK YOU HAVE TO DO TO GET TO THAT SHOW! They probably don't have many tours left in them and they wrote the book on how to put on a metal show. The documentary DVD Flight 666 gives a pretty good representation of what they can do to an audience.
There actually is a documentary about Iron Maiden touring with that plane: Flight 666