So far I have all collaborators invited and we are getting used to the new workflow with submitting/receiving changes, however, we cannot seem to share media. For example, I am using an .mp4 in a composition, but he sees the .mp4 but the link is broken. How do we fix this?
Chances are that whoever "he" is simply has hardware acceleration issues or cache problems preventing the MP4 stuff to be decoded. Impossible to say without the pertinent technical info. You haven't ven explained where the files are stored and how they are linked, so this is not going anywhere. You need to be much more specific.
It's definitely not a hardware/cache issue. As I stated in the OP, this is our very first project using Team Projects, and are complete novices as to how to set it up 100% correctly. The files he cannot see are stored locally on my machine, I imagine he needs his own copy. It seems to me keeping a shared Google Drive folder between the two of us to store media would be a good option right?