A few questions..

>How can I find out how many worker threads my FTP server can handle? I use cPanel & pureFTPd.
Trial and error

>Is there a way to issue a Touch command? If not, are there any plans to add this feature?
Right-click on the file, then select Properties from the context menu. Then change the last modified date.

>When I try to connect over SSH (sFTP), I get the following error when opening a folder:
Post the log from SmartFTP and from another SFTP client.