Hi Teresa,
Forgot to answer your question. You don't need BPM to achieve the above design. Just an additional inbound interface to be executed in sequence one without mapping (which does the pass through) and one new with mapping for getting the file name and populating it in payload for proxy.
Event based message processing is executed from PI. this does not suit your requirement. Here you need the trigger in ECC to read the file and send an email so this design can do the job.
If you want to try PI design, this is what I would suggest:
If in the email just needs total number of records and amount and this information is available, say.. in the last line of the file, then you can read the records as string with simple FCC, read the last line in mapping through a simple Java code and ignore the rest and populate it in the content of the email through graphical mapping with mail package API.
Choice is yours! decide PI and non-PI. 
Hope it helps!
Ambrish