In my experience, 2 devices will ultimately save you effort and frustration. Anything you choose as a good NAS/seedbox will be unlikely to have a good from the couch interface or handle Netflix reliable and easily. A small Android TV box may have a much better interface, simple app setup, and support all the streaming services, but probably won't be very powerful or convenient to use as a NAS. The NAS is always on, plugged directly into the Internet access point, and tucked away out of sight and sound. The Android TV or Apple TV box is silent, small, and can be mounted directly to the Beamer/Projector.
Yes, Kodi exists and it's add-ons can bridge this gap. But I still think that a SBC NAS running Jellyfin or plex + an Nvidia shield with jellyfin, Plex, Netflix, Spotify, YouTube, amaon, etc. will be so much easier to setup, manage, find support for, and upgrade.
I have a similar setup even though my server has a direct HDMI link to my TV. I'm not a fan of viewing using the server it from the couch. Setting up IR remotes sucks always. And it's confusing for anyone but me to use. But if my Nvidia Shield dies or I'm having network trouble, VLC a pretty good backup.