Localhost Developing

I do all of my development work on localhost before moving anything to production, and I’m wondering if this plugin will function from behind my firewall?
Or… will the Amazon API fail to respond to http://localhost/site-name
Do you not need a live running website before they agree to give you an API key, and how do you resolve that?