I did it via Airtable integration.
- It receives new member data (incl. label) from Ghost via webhook,
- matches each user with a list of emails,
- and send them via GMail (Google Workspace in my case) according to pre-defined schedule for each individual member (based on number of hours from sign up).
Find a step-by-step guide here: Ghost + Airtable + GMail: Send Automated email sequences to new Ghost members
Not to say that it is the best way, but works correctly with a moderate volume of emails. Relatively simple, no code, no zapier/make involved.