WordPress.org

Can I have the ZIP-file attached to the post too?

Yes. But you'll have to alter the source. Open wp-upload-unzipper.php and set $addZipToPost to true.

Can I keep the ZIP-file on the server?

Open wp-upload-unzipper.php and set $deleteZipWhenDone to false.

Can I disable the automatic extraction of archives?

Disable the plugin. :)

If you're thinking of contributing a front-end for this plugin, you'd want to check out $unzipArchives in wp-upload-unzipper.php.