What is the appropriate height for placing the TV?
The center of the screen should be at eye level when you are seated. For a living room, this is about 100-110 cm from the floor.
Can I reuse the same stand if I change TVs?
It depends on the new TV and its VESA standard. If the new TV has the same or compatible VESA and its weight is within the specifications of the stand, then you can reuse it.