Using Zapier to send emails to new and upgraded paid subscribers

Hi all … learning my way around the Zapier/Ghost integration and could use some guidance. The zap for a welcome email to a new free member is straightforward. What I’d like to create are additional zaps to send emails to (a) an existing member who upgrades to paid and (b) a new member who signs up initially at a paid tier.

I understand I can text-match on Subscription Tier Name but struggling with the logic/workflow for the various permutations here, particularly the setup for a zap for an existing member/subscriber who upgrades.

Also, is there a path to sending via my domain mail/Exchange Online vs Zapier mail?

And all of that said, is it better to use the Stripe integration with Zapier for this?

Thanks!