Can you create a single automated welcome email without an upgrade to the Mailchimp Standard Plan? Yes, you certainly can!
This functionality is free and allows you to edit the email as desired, and to include a link to a lead gen resource. If you need more sending options, like segmentation or scheduling, you are also given some advanced settings.
To add more emails to the sequence, you will have to upgrade, however.
Here's a screenshot of the plans for your reference:
