There's no way to check for free space on remote filesystem. In fact SFTP protocol already supports that, but there's not many servers supporting the functionality.

Hi

A nice little feature with Synchronization preview is displaying if target folder, or both folders, have room for the files. So you're not stuck halfway thru the Synchronization with one folder/drive full.

You have all the files listed, just summarize them and se if they fit the target drive/folder.

One other thing, I'm guessing WinSCP is storing the saved sessions in the registry.
Can't it be stored in a encrypted file on the root of the WinSCP folder so I can use it on my USB stick. :)