Hi
am trying to implement aem html pages into amp+aem html pages.
i have answer for your questions.Please correct me if any .
1. is duplicate content an issue, or can the AMP and standard html pages share the same content? =>yes You have to implement separate coding for amp pages.
2. is there a best way to set up redirects to AMP pages on mobile devices, or is that done automatically? => if you are using specific amp component/mobile pages My Answer is "automatically".Else you are using same component so that u have to access differently
3. can one author edit both AMP and standard html pages in one go? => If you are using same component for both amp and standard html ->yes you can author once and use for both. else you have to author .