it improves the quality a bit, but as long as the player and the DVD are not 4K capable, you won't get 4K on your TV. I hope I could help you a little bit.
Yes, you can play ordinary CDs with the device. It supports CD audio, CD-R and CD-RW, as confirmed in the official specifications. Greetings back, Jürg!
Yes, you can play CDs. The player supports CD audio, CD-R and CD-RW.
The connection to a soundbar or TV is made via HDMI. The player has an HDMI output, which is used to transmit audio and video signals.
The BlueRay player is connected via an HDMI cable. This assumes that your TV at home also has an HDMI connection. Most Samsung TVs have this - unless they are 10 years old ;)