Hi Bill,
There a a hundred and one ways of mixing down to your "final" stereo track, and I'm not the best person to advise to be honest. I don't think you are a million miles away though.
I do this:-
Build my project, which will be a combination of MIDI driven soft synths and recorded audio tracks.
I will route some tracks through separate busses, in order to apply various effects.
I will listen, and listen again, and again, tweaking levels, applying EQ and dynamic compression as I think it is needed, if at all.
I'll leave the project alone for a few days, or a week or so.
I'll revisit the project, and listen again. I sometimes find that, after not hearing it for a week that I still need to tweak things.
When, and only when I am absolutely sure, I will export to a stereo wave file. I'll burn it to a CD so that I can listen to it on a few different sources. If I find that I've messed up the bass, or what ever, I'll go back to the project and tweak some more.
As for mastering... I generally do that outside of Sonar. I still like to use Sound Forge for that.
So, that's just my take on things, and as far as I can see, you are not really missing anything. The export function requires that you experiment a bit, and decide on what is best for you. You can export just selected tracks, or buses. I route everything, eventually, to my Master Bus, and it is that bus that I export. If I don't want anything to appear in the mix, I mute, or archive the track.
That's just for starters... an expert will be along soon :^)
(LOL... as per usual, I take so long typing, I'm beaten by two posters this time...)