Which laptop to stream Spotify to integrated amp via DAC?

I’d like to get the cheapest laptop possible to stream Spotify via DAC to my integrated amp.

Is it safe enough to buy a 2013-era Macbook Air or notebook be safe enough in terms of its OS not becoming too old to support this, or should I buy a brand new one? It just needs Wifi (for Spotify Connect) and one USB port. Do I need to care about the quality of the laptop’s soundcard?

And I assume a Chromebook wouldn't work since it's not a Windows OS.
You don't need to care about the laptop's sound card if you intend to use USB.

Is the laptop's sole purpose going to be for Spotify playback? If so, you might want to look at a Sonore Microrendu or other NAA that supports Spotify connect. 
As for me, I only tried to use Spotify music on Chromebook via the USB stick. And to do that, I use the Spotify Converter and refer to the post from https://www.drmare.com/spotify-music/get-spotify-on-chromebook.html and then I can easily get Spotify for offline listening on my Chromebook.
To stream Spotify to the integrated amp via DAC, you can get help from AudFree Spotify Song Downloader, which can download and convert Spotify songs as local files. And then you can directly use the USB stick to stream Spotify to the integrated AMP via the DAC. No need to use a laptop and don't need to care about the sound output of your computer.