1. I think that would indeed be the best option.
2. The main concern is alerting. We are using the MSP pack, and would allow customers to schedule their own instances. Right now an MSP customer cannot change or add maintenance in site24x7. This would solve that.
3. I don't know the internal application logic, so what I am saying here might make no sense. But it might be a good idea to configure this in the Threshold and Availability section. Where you can toggle instance stopped state as being DOWN or not in a threshold profile. And maybe allow it to be overridden at the instance level.
4. Scheduled maintenance does not count towards our SLA, so that would be fine.
Thanks for taking the time to review this!