totally correct... but keep in mind that the hits counter will not be working...

Yes, but you don't need to upload a "real" file in K2 (since your actual file will be stored on S3) - nothing in the code will upload the file provided to K2 to S3 (although this would be a nice feature for future versions of K2, similar to JomSocial, etc.)

At any rate, you can simply upload an empty text file or similar tiny file to satisfy K2 (or modify code not to require it)

The 'Attribute' is the link to the file on S3 and when someone clicks the Link title it will now pull from S3, not from K2.
alp is right, download counter will not function without further modification.

case, do you have any ideas what would be the "further modification" to achieve the hits counter working for on external downloads? i really need this for a site, and if i can't accomplish it with k2 i will have to move to sobi2 or some other cck to have this feature, but i really like the flexibility and user friendliness of k2, so it's a hard decision for me. i really hope that it can be done with k2...