I am an active or an ex member of most of these groups for the last 2-3 years.
Most of them tend to start on a high note and turn into a graveyard with PH spam links and barely any activity or benefit to the users.
If I were to do this, here's are a couple of things I would keep in mind.
• Make it private, not everyone gets access. Only screen and qualified folks
• Higher barrier to entry- active PH activity could be a good proxy metric
• Set ground rules about the engagement, if someone is opting for launch support they should ideally share their pre launch planning and should share results post launch.
• Mandatory custom offer to all members by the product launching.
• Allow support and personal DM to members. ( if anyone has issues with personal DM don't include them)
• Mandatory whatsapp broadcast group, no other channel with get the justified traction/impressions required to hit #1