This integration allows you to stream music through wi-fi speakers compatible with Spotify Connect like Amazon Echo and Bose SoundTouch. The Sonos API does not currently support Spotify Connect. Requires Spotify Premium subscription. Bluetooth speakers are not supported.
For Smart Remote, we have an integration that controls Spotify, which uses connect API that is open only to premium account. (Freemium account can only use this API to get current played track for example, but cannot control anything)
For sonos, It is Spotify that has an integration of his service into the Sonos music provider ecosystem, and it is open to all Spotify users. (freemium and premium)
For your instance, using the Smart Remote and Sonos speaker, you will be able to configure your freemium Spotify account in Sonos application, then control your Spotify account through the Smart Remote Sonos control.