Can’t help you with any of the other stuff, but to answer your 4k question: No, you still need your 4k collection for best quality. Upscaled 1080p is still 1080p, it just makes it not look wonky on a 4k display. Any details lost due to the source resolution will still be lost, you can’t create extra detail out of thin air.
My guy, Windows itself has a fuck load of telemetry. They don’t need to include this in Defender.