Another thing, so after the event is over, the Starro infested Central City remains. After that, it will only be available to enter by player characters CR218+. Will it be opened up again to all next year? (and on that note, will the Age of Justice war-torn village be re-opened to all in June?)
No, the event is/was limited time. AoJ event will not return, and neither will Starro after this year. The event is only for the current DLC/Episode.