During setup, I declined to connect to WiFi and then set the TV to automatically switch to HDMI 1 when it turns on, and to honor CEC over HDMI so that my external AppleTV box can power it on and off. Taught the AppleTV remote how to handle the volume on the TV, and that's it. The Roku remote is in a drawer, and the TV behaves as a dumb monitor.
I'm not even sure whether it's possible to buy a large TV without software loaded on it, but you don't have to let that software run!