Im confusing about reading vu meter. I thought you were suppose to keep mix below 0. I was watching Eric valentine video, his meter jump to +3 when his kick hits in the mix. I'm wondering should the mix be near 0 vu for for most of the tmix and the dynamic tracks can go above 0 such as kick.
You shouldn't be keeping all levels below or at 0VU. VU is designed for metering dialog in a calibrated environment, not full level audio/high bandwidth content. When I have some time I'll write up some level information that is Nebula specific. In the meantime with a little substitute, you should be able to get the info you need from this http://rhythminmind.net/1313/?p=3224
Im currently using this http://www.klanghelm.com/products.htm. I assumed that being below 0 was the only way to make sure there is no distortion in nebula. So is it okay for stuff like kicks and snare going above the 0 mark.
It really depends on how the program was captured/setup. Not all Nebula programs are made to function at standard 0VU operating levels. Many are expecting to see near full scale audio. I can't give you a blanket "one size fits all" setting to use. Keeping everything at 0VU to avoid distortion is like always driving 20mph to avoid a speeding ticket.
To correctly use Nebula programs you need to know What dBFS level = 0VU for each program. Ask the developer if your unsure. Example - If your using one of my -20 NAG tape programs for a mastering session -20 dBFS = 0VU. So from here it is simple math. If you want to drive the tape +10 over 0VU you would send it a -10 dBFS signal.