Tying two blogs together

Hi there- we’re looking to set up a second blog where users can submit entries. Easily post text, images, photos, quotes, and videos.

All the entries are under a separate blog, but users can log-in and entries from one blog can be moved to another.

You can see the implementation on a site like: https://www.buzzfeed.com

Any suggestions on how to go about doing this?

We’re wondering how to keep our content and the user submitted content separate, but have the blogs interact with each other.

? Users can easily post text, images, photos, quotes and videos.
? Recent comments from both blogs appear on the sidebar.
? Entries from the second user generated blog can be moved to the first blog.
? Single log-in for both blogs, or log in via facebook.
? Users are required to categorize their blog entry.

Any recommendations would be greatly appreciated, thank you!