I cannot find what is the respective download limit for the various plan. Apparently, the download limit for a free account is 800MB. What are the download limits for the paid plans?

You can find the info in our pricing and plans page.

Please note DriveHQ has bundled Online Storage, Online Sharing, Online Backup and FTP server hosting, web hosting services into the same premium packages. So you can visit any of these sections and find the same service plans. For example, you can visit:

http://www.drivehq.com/ftp/ click on Pricing and Plans.

In general, if you order x GB storage service plan, then you get 4 times x GB of download bytes/month, which is far more than enough in most cases.