How do I get Email Marketing, and how many emails can I send?

Growth includes Email Marketing Starter and Pro includes Email Marketing Growth. On Launch it's an add-on: Starter is $29 a month and Growth $59.

Starter holds up to 2,500 contacts and 10,000 emails a month; Growth holds 10,000 contacts and 40,000 emails. The count resets on the 1st, and anything over waits for the 1st with nothing charged extra. Your first campaign goes to 500 people at most; once it finishes with few bounces and spam reports, bigger sends open up.

To be honest about where it stands: the add-on can't be bought yourself yet (Add-ons shows Tell me when it opens), and campaign sending opens soon. You can already build your list, write emails and send yourself tests.