Hi,

no, it only supports 2K, 1920 x 1080p.
Netflix is pre-installed.
No connection for the headphones is available.
If you connect the unit to the TV, the TV is only a playback screen.

Sony Europe

4k? No, 1080p FullHD at the most.
Netflix? Yes, according to the Sony website, this should be possible and is pre-installed on the device.
Old TV? The TV only needs to have an HDMI input, everything so-called "smart" is done by the player before it sends a ready-made picture to the TV.
Headphones? No, no connection for cable headphones, no Bluetooth for wireless headphones.