It's possible. I've had Samsung and LG TVs that I've left disconnected most of the time and used them with external boxes like the Nvidia Shield, Apple TV, PCs and game consoles.
I've used wired connections or temporary Wifi network in order to prevent the TV from connecting to the internet without my knowledge.
I was able to update the firmware on my LG TV by downloading it and loading it onto a USB drive. Some firmware updates may improve picture quality or compatibility with external devices.
One annoyance is that there may be buttons on the remote that launch built in internet connected apps. It's important to have a TV that can easily switch between inputs.
I've used wired connections or temporary Wifi network in order to prevent the TV from connecting to the internet without my knowledge.
I was able to update the firmware on my LG TV by downloading it and loading it onto a USB drive. Some firmware updates may improve picture quality or compatibility with external devices.
One annoyance is that there may be buttons on the remote that launch built in internet connected apps. It's important to have a TV that can easily switch between inputs.