Structure of multiple domains

I am beginning a project that involves 40 domains, each linked and sharing posts.

As a newbie I am struggling to come up with a plan for the structure of the network of sites.

I intend to use a single domain as a gateway where contributors will register and submit posts. These posts will then feed to the relevant other domains. eg, a post regarding a specific location will then feed to the domain for that location.

The main site will display all posts for all areas and will be the only domain offering registration.

My question is, do I install a multisite at the main domain, Each contributor gaining his own blog, adding the domain mapping plugin to include the other sites. If so, what do I install at the other sites and how do these other sites get the posts the main multisite bloggers submit?

Alternatively, should I install WordPress single sites at every individual domain and use a feed to post plugin to extract and display content from the main site. If so how does this effect SEO.