I know how to do the popup boxes with a prompt to ask for email. There seems to be no form of exporting emails to your mailchimp lists, but there is a fairly simple way to write to a file every email that is entered into the prompt, and from there, you may send emails to the addresses in the file. Also, I can do the Instagram hashtag feed fairly quickly and style it a bit. Contact me to discuss some further details on the website, such as the page so I may take a look.
Thanks,
Mathias