Best way to use Asana for a 2-person start-up

I have watched a few videos - more than once, but I still have questions about the best way to use Asana for a 2-person start-up. Specifically:

  1. I want everything to be public between my partner and me (I do not want to mark everything public). Is there a way to set this as a default?
  2. It’s not clear to me how my emails interact with Asana. Help.
  3. Should I keep files/documents in Asana or elsewhere (Dropbox) and attach to a task when needed…that said, a primary project/task is a document. What is the best was to handle this?

I do not need all the bells and whistles. Is there a video or guidelines for start-ups who just need basics?

Thanks, Celia