I’m trying to remember more details.
Ray Wise said David and Mark were working on it formally for years before it was announced. On the original TP Complete Mystery set, which was like a year before S3 was announced, Ray said the bonus feature meeting between David, Sheryl Lee, and Grace was filmed a day or two after David’s first formal meeting with them about S3. He said David had been mentioning it to him happening for a year or two before that.
Before the official announcement, Ray, Sheryl, Kyle, Grace, Chrysta, Catherine Coulson, and Michael Hawk were the only cast members that knew it was being made. It was a surprise to everyone else.
Also, David is good friends with the entire cast, and they’ve all been in regular contact with him (and each other) since the original series.
Oh, Laura Dern charmed the pants off everyone. Her and David seemed like super close friends and he treated her as his equal. David calls everyone by their character name, even irl sometimes, but he always calls Laura “Peanut.” Not even Kyle got a special nickname.