Hi and welcome!
Usually, the problem with the Edit option being disabled is because the default editor app cannot be found. Even though you have selected BBEdit from the popup menu in the Preferences, Yummy will ask Mac OS X where BBEdit is installed - if the OS says that BBEdit isn't installed then the Edit option will be disabled, and this is where the problem starts... The OS can 'lie' about whether an application is installed or not if the app is not 'trusted' by the OS. This is a newish security feature of Mac OS X.
To get around the problem, try the following:
1) Quit Yummy FTP
2) Make sure your BBEdit is installed in the Applications folder of your Mac OS X system disk.
3) Launch BBEdit, create a new document then save it to the Desktop. Quit BBEdit, then double click the document saved on the Desktop to launch BBEdit again.
4) Launch Yummy FTP
The Edit option should now be available.
If you continue to have difficulties, please contact me via email (support at yummysoftware dot com) so that we can discuss the matter further.
-Jason