Guys, I know you'd like to argue your way out of this and find exceptions etc. etc. But i didn't make the rules.
Thing is, if you want to comply with the law that means you need to have a full set of stuff, if you are storing or processing European Union citizen data.
Or you can ignore the law and expose yourself - dependent on your location in the world and your business scope that might not be such a big problem.
However, if you want to adhere to the law, do it fully and in a clean way. Everything in between doesn't make sense.
What if I want to capture emails from a Shopify Store newsletter?
What's the question? If you want to make money from that Shopify Store, you need to get paid somehow by Shopify. That means there's a legal business (even if a single person), there's a registered address etc. You need to make that information public. And yes, an email has clearly been classified as "personal data", so if you capture it, the law applies.
By the way, it also applies to Shopify, to your mailing provider (Aweber, for instance), the hosting provider etc.