4.5.2 is released.

In Conditions tab, choose condition by value and compare [PAYMENT_GATEWAY_ID] with the numeric id of your offline gateway with comparison "=" as additional condition to only auto-email to those who choose offline. Of course other conditions on the payment basket need to be added in the first "Basic" tab in triggering conditions, and "Relative to this date" should be one of the date of latest payment basket for those payment basket substitutions to become visible and available in the conditions tab.

Your condition looks correct. Just be sure "1" is the actual ID of your payment gateway which you can find under the "Id" column in CBSubs > Gateways on the far right of the table. It's not the number under the # column.

And to confirm, the cron needs to be enabled/set up for all Mailers? So even of the conditions are being met the system won't check to send emails unless the cron fires?

You only need 1 CRON task setup for CBSubs Mailer. Just have it call the URL supplied in CBSubs Mailer > Automation Settings by the "Url of cron task to both process mailer rules into queue and then to process mailqueue" parameter. Run it once daily and you should be covered for all mailers.