How can I set up ftpd to run when my computer restarts and how can I turn it on for port 5021? Mac OS X 10.7 Lion doesn't have a checkbox to turn the ftp server on anymore.
As you noted, Lion doesn't have a checkbox to turn the FTP server on anymore.
However, the back-end (ftpd itself) is still there, and you can still enable it manually from the command line by telling launchd to enable and load the existing launchd entry for it or simply running ftpd manually (cf. this thread on MacRumors). Consult the launchd, launchctl, launchd.plist, and ftpd man pages for details, but the basic command to start the ftpd server on the default port is:
sudo launchctl load -w /System/Library/LaunchDaemons/ftp.plist
As was suggested on the MacRumors thread, you may want to take this opportunity to migrate to SFTP or another more secure, better-supported protocol.