On the original topic of this thread, I started my King journey in the very early days (relatively speaking) of the early '80s, so hard to be objective about where I think a good place to start would be.
One possibility is to start with Night Shift, read those short stories and get a feel for King's early writing. Then maybe go to some of the early novels and work your way forward.
I would wait to start Dark Tower due to its length and the different sort of story it is compared to most of his work.
Also, I would recommend reading all the Dark Tower related stuff first, then read the Dark Tower. That's how I read it, sort of unintentionally at the beginning, but I liked how that worked out.