GMA3 has been kicking around for a while. I want to say it replaced "The Chew", but I'm not 100% certain. It started as something hosted by Michael Strahan, Sara Haines and Keke Palmer (?) as a GMA brand extension in the afternoon - the vibe I recall was somewhere between Hour 3 and Hour 4 of the Today Show. It went through a couple of mutations with hosts coming in and out until the pandemic hit. (GMA can't do an actual 3rd hour, with Kelly 'n' Ryan firmly ensconced there.)
Early in the pandemic, it was replaced by a daily newscast at the time called "What You Need to Know" which was hosted by Robach and focused on COVID news (vaguely like Nightline's origins, for those old enough to remember that), I'm not sure exactly when that show took on the GMA3 branding and morphed back into an Hour 3 of GMA, I think it was the fall of 2021.
As for Question #4, I think the answer to that one is black and white.
John