In order to build a Progressive Web App, the following minimum requirements should be met:
A secure connection (HTTPS) over your site makes sure all traffic is as safe as a native app. A secure endpoint also allows the service worker to securely take action on the behalf of your app.
The site should be controlled by a W3C manifest that determines the experience and behaviour of your PWA. This includes everything from images, to language, to the start page of your web app.
The Progressive Web App should have a mechanism (e.g. through a service worker) to help control traffic when the network isn't there or isn't reliable. The app should be able to work independent of network.
The site should be responsive on tablets & mobile devices.
Each page of the site should have a unique URL (individual pages are deep linkable via URLs e.g. to share on social media).
The quick start will provide the tools to address some of the above requirements, like building the W3C manifest and enabling network independence. However, it is responsibility of the site developer to fulfill the other requirements.