Hello, 

Instead of writing insert code to insert the data source  , you create a data source of your own manually and how glide  the the same data source every time using glide record and pick up the latest record attached to it and get the sys id of the attachment and parse it and load it using the same piece of code which you mentioned above

OR 

After the transform map runs , glide record the data source and remove all the attachments attached to it through script by gliding attachment table  and then next time when you submit the record producer  again attach the new one to the data source and  then glide record to the data source and  take that attachment and parse it and load it and then again delete it after the load .So doing this in loop through script will satisfy your second requirement and for info messages you can glide record the  staging table  logs in the record producer script and get the count of records which are having state as inserted  and display the count in info message after the load happens 

OR 

if things are getting complicated use one API called glide Excel parser which is the best and easy API to integrate with Excel which would parse the data in the excel  and insert it in staging table and then load it into the target table.  You can do this in your record producer script only. 

please refer to below link to see a sample code.

https://developer.servicenow.com/dev.do#!/reference/api/quebec/server/GEPS-getRow

Please mark this helpful if this answers your question!

Thanks