WordPress multisite or not?

Hey All! Been testing WordPress out as the potential CMS of choice my company switches to. At current we use a proprietary CMS that isn’t growing well with our site. A quick overview of our site is a Local News site, that specializes in hyperlocal coverage of everything in the community. In addition to news and sports coverage, we provide multiple blogs from various figures and writes in the community.

I have been going back and fourth between a single install of WP or a Multisite install. I have been doing tests with both, but where I am stuck is while I know Multisite is well suited to having many blogs (of which we have tons, all blogging on different subjects all together, but all under the same centralized umbrella site), we tend to do a lot with pulling the latests posts from all the blogs together in the same place, or featuring content from multiple blogs on multiple pages.

Additionally, we rely on the idea of searching everything on our site. Is Multisite even capable of allowing a visitor to search for a name or a tag and finding all relevant posts/tagged media items from across multiple sites in the network?

Finally, and equally as concerning, we want to be displayed as one united site in regards to SEO. How can we integrate sitemaps from various sites in a network to a search engine? What are the best practices in this situation?

Suggestions highly appreciated. I believe WordPress is the CMS of choice, but this is one of the big hurdles I can’t decide the best practice for.