I haven't had to change my filter rules since the filter process was redesigned back in May. It looks to me like Custom Filter Rules (directly below the 'Frequently used Filter Rules') may solve the forwarding to multiple email addresses problem. Only one email address can be in a rule but rules may be stacked.
For example, to process an email from Calibre with a 'USA Today' subject line, create three rules that all test for the subject ": USA Today". The first rule forwards to kindle 1, the second to kindle 2, and the third moves the email to a 'Sent to Kindle' folder.
I set a 2 week retention on my Sent to Kindle folder in case I have to resend the news. In my experience Amazon sometimes loses my news.
The delay on sending emails from Calibre to Gmail is controlled in the Tweaks section of the Calibre preferences. The tweak is called 'The number of seconds to wait before sending emails'. The description for the tweak reads:
The number of seconds to wait before sending emails when using a
public email server like gmail or hotmail. Default is: 5 minutes
Setting it to lower may cause the server's SPAM controls to kick in,
making email sending fail. Changes will take effect only after a restart of
calibre.