For anyone else who wants to do this, just set up the absolutely amazing Volumio on your RPi or any other computer. https://volumio.org/ The web app is great for use in your house, the Spotify plugin is first class - it's supported as a target in your Spotify app, or you can browse straight from the webapp, which means even a guest on your wifi can easily pop on and help pick the music.
What kind of audio output does a raspberry pi support?
https://elmwoodelectronics.ca/products/hifiberry-dac-rca?var...
For powered speakers you can get a DAC or you can use unpowered / passive speaker if you get a amp hat