Hi,
Perfect question.
Organic search is important because google pays attention on websites who have traffic from organic search.Just there is a key concept: you should choose right and relevant keyword.
Another importance is that visitors from organic search are more inclined to do purchase rather than those from other sites, which can be from not relevant ones. The main problem for organic search is that it takes time to build. What you need is some SEO techniques like white hat SEO :)
Well, E-mails... this is the most important factor for customer retention. You cannot do e-mail marketing and send the mails to those who are not your customers. they will take it as a spam. I would recommend to do e-mail marketing just for your customers. Well, for making them loyal.