1. Luckily, no.  This workflow will be instantiated after both files have been received.  

2. It's actually more than just tracking number.  Serial number, part number and a few others.  The tracking file will contain data for all POs in the main file.

3. The tracking file will be named the same thing daily, containing tracking information for all POs in the main file.  There are not multiple files (for either one).