They are related but not the way you think.
When you turn the brightness up contrast goes down and response time goes down too.
If you use the lcd as a computer display you may need a brightness range from 50 to 150 cd/m2. If you use it as a tv display it should have >250.
Response time is a little bit difficult.
The manufacturers give you the time for black to white changes which is faster than grey to grey, especially for TN panels (twisted nematic).
VA panels (vertical...