Is there a size limit on files uploaded to Dropbox, Amazon S3, etc.?

Yes, the file size limits are as follows:

• Dropbox – 350 GB;
• Google Drive – 5 TB;
• Amazon S3 – 5 TB;
• Microsoft OneDrive – 10 GB;
• OpenStack Swift – 5 GB;
• WebDAV servers – depends on the server settings (usually 50 MB);
• FTP and SFTP servers – depends on the server settings.
• Box – depends on the type of account:
       ◦250 MB – Free Personal account;
       ◦2GB – Starter;
       ◦5GB – Business/Enterprise account.