Login Screen That Will Redirect To Multiple Blogs Based On Username

I’m currently running multiple WordPress blogs on the same database, each with their own unique login. I’m successfully using the Members Only plugin for each one, so a blog can’t be accessed unless you’re logged in to that particular blog). What I would like to do is create a login portal, where from a single login screen (can either be another WordPress install specifically for this use, or it could be html, php, etc.), a user will be re-directed to a specific blog based on their username/password. In addition, I would like to have a “master” username that can access all blogs.

I tried creating another WordPress install that acts as a login portal (using the Peter’s Redirect plugin)…however, while this redirects based on login successfully, it doesn’t work with the Members Only functionality, thus making all blogs accessibly to anyone that logs in…or, if I keep the Members Only turned on for each blog, a second login intervenes after the redirect.

So, here are my questions:

1. How can I set up a login portal so that each blog remains only accessible to the user logged into to it (user goes to main login screen, and is redirected to “their” blog based on login, without seeing another login…AND they can’t access any other blogs). It’s worth noting that each user only has subscriber permissions, NOT admin permissions.

2. How can I have a master username that accesses all blogs?

Any help would be GREATLY appreciated. Thanks!