There aren't any download or storage limits for your app (other than available space on the device, of course); if there were, they'd be mentioned in the iOS Data Storage Guidelines. However, you do need to consider how your data files will work with iCloud -- in particular, you should decide whether it's okay for the device to discard your downloaded data when storage gets low.
If it's okay to remove your files, store them in the caches directory. If it's not okay, then you can store them in the documents directory and set the attributes on your files to exclude them from iCloud backup. Also, be sure to store user data separate from the downloaded data so that the user data can be backed up.
With so much data to download, you should consider using the new NSURLSession network API so that you can download data in a background session. This avoids the need to keep the app running while the data is being downloaded.