Re: How long should the new series go on for?
7 Films. Tell a complete story, an epic one, but complete it, don't let it run into the ground and hope for a revival like the Bond films have had, especially as, unlike Bond, one of Batman's best stories is his origin story, and so everytime it goes down, the next team is likely to reboot it, especially if other properties it's connected to ie Superman have been rebooted.
Tell the Quintessentail ultimate Batman saga. Do it.