Multi-site or Domain Access for 250 Chapter Sites

I am in the process of setting up 250 chapter sites for a client. Each will be identical in functionality and themes, and all Drupal updates will happen at the same time. Each chapter site will be mostly independent from each other, although there will be a master admin that will have access to all sites, and there will be some calendar information from the national level that should show up on all chapter sites. Each chapter site has members which will be able to login into their chapter site, but should not be allowed to login to other chapter sites. Each chapter site will have its own admin which can create new pages and calendar events.

I am trying to figure out the best way to set this up. I am looking at either a multi-site setup or using Domain Access (but if anyone has another suggestion, I am all ears).

As I see it, using Domain Access will make it easier for the master admin to create new chapter sites, to apply Drupal updates to all sites, and to administer all sites. I am concerned though about having all 250 sites in one database and any issues that would cause for security between sites, scalability, or issues if data should be corrupted on any one site. I also wonder if all of the user interfaces in Domain Access will scale to 250 sites (will there be long lists of checkboxes which make it really hard to use).

The mutli-site setup has separate databases for each site, but will need some custom scripting to do a drupal update on all sites, to create a master admin that can login to all sites, and to replicate national events to all chapter sites.

Any advice out there on how to set this up?

Thanks,
Matt