Shopify > Mailchimp Automation Help

I'd like someone with some experience to help me with some Mailchimp Automation. I'm after: 1. Ensuring all the orders who tick the newsletter sign up go to a Mailchimp list. 2. Setting up an automated campaign where any customer who purchases items over £20 is emailed about a review and competition. 3. We offer customers the ability to order sample products, but have found that a lot do not come back to make an order. We’d like to setup a retargeting email campaign that sends 3 emails after x amounts of days / weeks to follow up on these sample orders. I can do all the templates for you, it is purely setting up these automated campaigns so they 100% work. Basically I want to ensure anyone who buys from our Shopify store goes into a list for newsletters, and is either targeted with a review email or a sample order follow up process. If one site is done successfully I have 5 others that would need looking at also.