Instant thought: I'd use Dropbox for file storage rather than google - using the dropbox public file function (it gives a public url to the file) makes updating/changing a snap.
Also: CBR / CBZ files can be downloaded into a comic book reader on an ipad (as epub files can be downloaded into the iBooks app) so I'd suggest making PDF AND CBZ/CBR (or ePub) available.
On drawback: I haven't checked, but is the paypal pay via mobile option america only?
-pj