1) There are several modules listed as "not installed ('require" failed).
Are these things I'm supposed to have?
No, that just means one of the optional components SA can use was not installed.
Some features of SA use add-on perl modules. Bayes uses DB_File, for example. If the modules aren't present, that optional feature of SA is disabled.
2) Since I am calling spamassassin from MIMEDefang, shouldn't /etc/mail/sa-mimedefang.cf be listed somewhere in here as a config file?
No. SA itself is not aware of, and does not care about mimedefang.
As far as SA is concerned, mimedefang is just another program calling SA. But when you run spamassassin --lint, it's your shell calling SA. SA doesn't care about sa-mimedefang.cf any more than it cares about your .bashrc.
3) What does "debug: plugin: Mail::SpamAssassin::Plugin::URIDNSBL=HASH(0x84d9340) inhibited further callbacks" mean?
Debugging information. It's got to do with which plugins want callbacks and which don't. Unless you're writing your own plugins, it's not of concern to you.
4) Is there anything else in here that doesn't look OK?
debug: diag: module not installed: Net::DNS ('require' failed)
You might want to consider installing Net::DNS. SA needs that to query RBLs. It's optional, but I'd recommend it.
Other than that, it all looks good to me.
