Requirement is to create a domain and verify the domain in mailchimp. Then by creating an Api key it should be able to use MANDRILL app API calls. Welcome emails should be sent to the users signing up(subscribed by default). Also, the unsubscribed users should not get anymore emails.
I can manage your email marketing that will make your work much easier and will help you to get more exposure by providing you with catchy and helpful content for your possible viewers and customers. I have worked on MailChimp in past and I love Email Marketing