Network Installation, Sitewide Tags and Queries

I’m building a network that will encourage authors to start their own blogs. On a page of the main site I would like to, among other things, list the titles of the sub blogs with a custom description that I write myself.

I’d also like to have users click on individual authors and send them to an author profile page, that I write myself, but that pulls data from the sub site as well.

I’m aware that the Sitewide Tags plugin is the best place to start.

I’m looking to add some of the data for the author profiles through custom post types that I create in the main site, along with custom taxonomies that I create.

But I’m also looking to pull some of the data for each of the author profiles from the individual sub sites. For example, their blog name, the date they last posted anything and their country of origin, from a customized user field from the dashboard/user area.

So for example, on the authors page there would be:

Author name, blog name, last post date and country of origin, plus a thumbnail I create and tags I create.

The individual author pages would include a background that I write, along with the data above.

Is it possible to grab that type of info from a sub blog, from separate places? Is there a list of queries anywhere that are possible?

Maybe a more important question: is there any data that cannot be pulled from the sub sites?

Thanks very much in advance. Everyone has been great.