I did not find an official file with asin in it in my lib (some handmade ebooks had however)
About the 10 times same number, I did not know it either, but you can try some at:
http://www.isbn-check.com/
Background function seems nice. (is it in build 8840?) I myself would prefer a way you could modify the order in the settings. Sometimes you just want to work in an other way than normally.
Reverse scan for last pages would be great.
If this slows down the process, you could maybe add it as an option in your settings (while it seems you will have to rebuild it all, this could be a good moment if you want to add such option)