I can only give you half an answer to half your question I'm afraid
In the options for spam guardian it asks you for two email addresses. one where spam can be found, and one where ham (non-spam) can be found.
I created mailboxes specifically for this purpose.
I then made the spam mailbox the "blackhole" mailbox I configured in all domains I have control over personally. This basically guarantees that only spam will arrive in that mailbox.
Now, as to what to do about the ham mailbox -- well, I don't know. I suppose I could forward copies of non-spam emails to it from time to time, but I honestly can't be bothered.
And I think you really need to give spamassassin both ham and spam to feed off in order for it to work effectively.