1) see the following page for details on creating a record set, pay close attention to step 5 for details on setting up the filter:
WSc78c5058ca073340dcda9110b1f693f21-799ca.html#WSc78c5058ca073340dcda9110b1f693f21-7915a
2) in the download file server behavior, the drop list for triggers will have an option for recordset not empty, select that.
next to file name, click the lightning bolt and select the file name column from your recordset.