trem,
sounds like you are asking 'mastering' specific questions....
that is an entirely different thing.
i have a 3rd party software i use (Wavelab) dedicated specifically to mastering.
i use a 3rd party set of Plugins (WAVES) to use for mastering.
when i am going to master a song, i bounce it to a stereo file, 24 bit, no dither.
it is a 'what you hear is what you get' bounce directly thru the master bus, with all plugins and automation included.
then i "EXPORT" that 24 bit wav file out of sonar completely and work in Wavelab.
if you are going to try to master inside of Sonar (not my choice method) then i would suggest bouncing your song down to a final mixed stereo file, export that, and bring up a brand new clean 'song' file and import it into that, putting your plugins on the master bus and processing directly thru that, avoiding all the unnecessary processing in your working song. (even the channel strip eq's hog memory)