Gain Staging The Right or Wrong Way?

No, it is certainly not the way I do it.  I get all my tracks at the same rms level e.g. -14 for example. RMS that is.  When you say you adjust gain for -12, what is -12 then?  Peak.  That means all the rms values on your tracks are varying all over the place.
 
The all faders at unity and get the mix from further back is not my method of working either.  I don't like it.  It means you are sending a variety of rms levels in and out of plugins etc.  Especially on buses.  Not getting the best range for those plug-ins perhaps and certainly not the best S/N ratio either.              
 
I would rather have all my tracks at a constant rms level and have the faders all over the place representing the mix, especially visually.  If a fader is right down it tells me that track is only very subtle in the mix level wise that is.  You don't get that same visual feedback with all faders at unity.  When the tracks are all at a consistent rms level too you can get those levels very consistent going in and out of every plug-in on a channel for example. Which I feel is better.
 
Here is my take on it anyway if you are keen:
 
https://drive.google.com/file/d/0B_2Jb7O_b5BkODRTMXNjX29IaEE/view?usp=sharing
 
 
 
 

-20 on your master buss is a nice ref level for sure.  I work at both -20 for more pristine things and -14 for a lot of more general work projects and duties.  But what is going on with your tracks though?  rms wise sounds like they are all over the place.  If you keep your track rms levels constant then the peaks that are in the attack transients will be all over the place instead.  Fine.  As long as they don't crunch into 0dB FS that is.  And they won't because of the built in headroom you have chosen along with your ref level choice.  
 
Tracking at a constant rms level is easier too.  Just adjust the input gain on the preamp on the way in for a nice 0 dB VU reading.  What could be easier than that!  There are often a million questions about how to adjust incoming record levels.  This is way simple.  It works and sounds great!  It is the percussion sounds you have to watch though, and that is when you start using your peak meters more.
 
I have recently got the Waves Dorrough meter for $29.  This is excellent.  As well as lots of rms info it displays peaks in a rather incredible manner as well.  The free (was free anyway!) Waves VU meter also has a superb ballistic.  Uncanny like the real meters.