That sounds like a good approach. Also, maybe your vote and voice can make a difference in this feature request: Petition for being able to "deselect ALL" member notification checkboxes at once in the 'member notification settings'. Being able to (de-)select all notification checkboxes would sure make managing notifications for existing users less time consuming.
And you have the right plan for it (Enterpise[+]), it might be worth including tasks to go through notification settings in a welcome project through custom onboarding