You can load the data and utilize filename() function:
LOAD ..., filename() FileName FROM sales*.xls ...;
From the FileName, you can cut the year and week part, and use function MakeWeekDate(YYYY, WW) do create the date. You can do it right there in the initial load if you wish.
And, store this into the QVD. Of course you have to concatenate the "Data" table to the existing QVD before storing.
As fior the incremantal load... I did something similar once using this way - after the files were read from the folder, I called a batch from the script that moved all the files to another folder. Maybe there are better ways.