1- You should first ask yourself, why do I want to normalize? And if you say Lead Vocal or Choir, you are talking about separate tracks in Cubase?
2- Normally you normalize to a value, so in your example you have 10 dB headroom (from -10 to 0) so you can increase the peak value to anything between the two. So a negative value between -10 and 0, though is never recommended…
3- Again, why normalize? Read at Bob Katz’s site all about mastering.