A good starting point for background, ambient audio is to set the levels around -24 to -34 to start with then adjust according to the rest of your mix

All dialogue should average around -12 dB (give or take a range of 4 dB)

If you are looking for impact relative to the average audio range then -6 dB is a good range for spot effects - ie. a gun shot, a door slamming, etc.

You have run out of audio information at this point, the export will crunch the data and you will have terrible sounding distorted audio

Contact a Post-Production Support Specialist