How could I best send a mass email to a variety of contacts at any given time? (like mailchimp…)
As you have rightly suggested you will need to use some service such as Mailchimp
You would also need to use a service such as Zapier to integrate both Mailchimp and Airtable together
If you are using a workspace that has access to Blocks (Pro and above), there is also a SendGrid Block that integrates with the SendGrid service API.