1. The question everybody wants answered... "When is the next book coming out?"
Where have you been? They're all out now! Go get 'em!
Marvel Comics is currently running a Dark Tower adaptation as well. Parts of book 1 and book 4 are featured. While I was hoping for new material, it's quite nice what they're doing. Ask your local comic shop for back issues.
My suggested reading order is more or less the publication order. Dark Tower books in bold, other required reading in normal. Optional books in parenthesis.
(Jerusalem's Lot) - short story
('Salem's Lot)
(The Stand)
(Eyes of the Dragon)
(The Talisman) - Required to understand Black House.
The Little Sisters of Eluria - short story
The Gunslinger
The Drawing of the Three
The Waste Lands
Insomnia
(Rose Madder)
(Desperation and the Regulators)
Wizard and Glass
Hearts in Atlantis
Black House
Wolves of the Calla
Song of Susannah
The Dark Tower
If you'd like to know why I say Insomnia, Hearts in Atlantis and Black House are "required" reading, take a look at the questions regarding them on the left hand side. I think you'll be surprised.
The long version of the answer to that question involves King's influences, specifically H.P. Lovecraft. Lovecraft had two storylines running through his works, the Cthulhu Mythos stories and the Dreamland stories. King is essentially doing the same thing with his works, having the Dark Tower stories and the Crimson King stories.
While the Dark Tower finishes out the Crimson King path, it won't be really clear what is going on unless you read Insomnia, Hearts in Atlantis and Black House.