Customer reviews are the "social proof" that encourages people to join in on something. It's one thing for you to tell people to sign up for a campaign, but it's another thing for your happiest customers to say it too. Publish your best reviews from communities like Yelp right to your website. This adds genuine value to your landing pages when people are on the fence about submitting their contact information.
Some readers will unsubscribe from your email autoresponder, whether it is short or long in duration. It is inevitable. Watch for trends that might indicate a necessary change (e.g. high unsubscribes after a particular lesson), but understand that unsubscribes are a natural part of your list’s equilibrium. Even if people unsubscribe, they were exposed to your content before they did so. Load the beginning of the course with excellence and go from there.