Hey Jay, great that you've started. As you say you can catch up by reading/listening to a bit of Parts 1 and 2 while you continue. But be sure to read all of week 1 first before you go back to catch up.

I don't really get the addition of, "in this" to the breathing mantra

I interpret this as meaning I (both the imaginary little i, and the one true self) am here now, in this dream of life.

Con amor