Since the filmmakers are supposedly going to split the story into three movies and two six-hour miniseries, how would you like to split it up? I have heard that they want to save the W&G for the latter portion, but I think an ongoing back-story would help break the story into a multifaceted, layered production.
I think the best course of action would be:
Movie 1: The Gunslinger
TV 1: Drawing of the Three (Wizard and Glass)
Movie 2: The Wastelands (Wizard and Glass and some comics)
TV 2: Wolves of the Calla, Song of Susannah (Comics back-story snippets)
Movie 3: Dark Tower
I think that the first book, as is, would provide a perfect cinematic introduction to the series. It would be nice to have an expertly woven series of flashbacks (something I thought Lost taught us how to do well) that break up the story well while simultaneously providing a thematic respite from a potentially monotonous linear story. I think that the first novel is perfectly structured for the initial entry, and tacking on the Drawing of the Three (or even the Wastelands) to the first film would be at the same time anticlimactic and overstimulating. I think that the first novel tells us a lot of the information we need to continue. To let it stand on its own with its own specificity and integrity will make the rest of the story enticing for critics and audiences alike. There is a lot going on in The Gunslinger, but we often forget this because of the enormity of the rest of the series. Let this one be subtle, character-driven, and gritty before the rest of the story explodes in action and introduction of so many characters.
I think this flash-back format would work well for all of the back-stories (Roland's, Jake's, Eddie's, Susannah's, Jack Mort's, Callahan's, Ted's, and any other character we wish to see fleshed-out in the extended multiverse). The tiny flash-backs in the first movie would prepare us for the overall motif, and then the flashbacks could expand to become what they need to be story-wise.
For the first miniseries, I think that the W&G flash-backs could work well, initially, as blood-poisoning hallucinations and then continue as fire-side stories for Eddie/Odetta. The miniseries could culminate with the great box canyon shoot-out and the showdown between Detta and Odetta.
There is an unspecified gap in time between Drawing and Wastelands, which provides a natural break leading into the second film. The Wastelands movie could stand as it does, but continue past the Blaine debacle and finish with the showdown in emerald city. I think the flash-backs could incorporate the Long Road Home storyline (introducing us to a powerful Crimson King) and end with the final tragic flash-back at the end of Wizard and Glass.
Another unspecified time-lapse, and we're into Wolves. Like the majority of Wizard and Glass, Wolves takes it's time in getting to the action, which may be easier to absorb with the assistance of the length of a miniseries. It could go into the Song of Susannah in the same way and possibly end with the same cliffhanger. I think that the flashbacks could incorporate Callahan's story, along with the story-lines from the Fall of Gilead and the Battle of Jericho Hill ... perhaps to a lesser extent. Although, I would also like to see this series do something concrete with Rhea, Farson and other untidy portions.
The Final Dark Tower movie could stand on its own, with whatever revisions the filmmakers want to make for cinematic purposes.
This format would really only change the placement of Roland's purging confession about his history in Mejis, but I don't think it intrinsic to the story to delay it until later in the series. I would actually prefer for the miniseries to be a regular series, albeit cable-length (12-13 episodes per season). I think that this would allow the story to unfold at its own pace. This would also open it to wider awards consideration, expanded audience awareness, and greater DVD sales. This could also assist in the bridging the chasm from TV to movie specifically--which is going to be hard no matter how you slice it. It's easy to have a recap each week before an episode, but a "previously on" intro could be hard in the movies. Some sort of classy montage perhaps?