While I feel I've come a long way in step recording, sequencing, etc., now that I'm recording a bit more live audio I return to the basics:
When I'm setting input levels ready to record -- should I let input level readings barely peak into the red a bit, on a track and/or master etc., or is any red at all starting to clip and you want to peak max. still in the green never into the red, because any red at all is bad or clipping?
Thanks in advance - Jeff

Red is bad and will not sound correct. Don't have to record that loud. Usually peaks of -6 to -12dB. Every track you add to a total recording adds volume to the Master track or output or bus. You usually have to perhaps end up turning down track volumes at the end when playing back the entire score or all tracks.
 
Never in the red, and even the end mix is never in the red. Although computers may and I stress - may handle up to 103% and you may peak into one red bar briefly and not hear it, it is not preferred because that is the way computers are. You will end up wrecking the track if going into the red when recording, and the sound is not good at all. Nothing like analog at all.
 

Nothing like analog at all is correct, but you won't distort until you reach 0 dB. It won't sound bad if it hits the red a little; most of my recordings do, but if you're recording using 24-bit depth, -12 to -6 is really all you need. I read here that it provides more 'headroom', although I still don't really know what that is.
Just watch your Master bus (or Mains if you're not using a Master bus, which you should be using) to ensure that the summed audio is not reaching 0 dB.
From the SONAR X 3 Help files:
"Note: Because SONAR is a digital recorder, a level of 0dB indicates digital zero. Digital distortion will occur at 0dB. You will not get analog compression or warmth from pushing the input levels."
 

I used to not worry about the occasional red, but now I stick with the -12 to -6 peaks.
Remember, you can't unclip a track. You can play it quieter, but the clipping is still there. A distorted electric guitar may mask it some, but it can be fairly obvious with cleaner sounding instruments.
When recording, I stick to a fairly absolute -6 max.
As your project develops, some effects can exaggerate mild clipping, and you may find yourself fighting clicks and gritty, scratchy sounding tracks.
Also, as noted, levels are cumulative. You may have individual tracks peaking in the -18 to -12 range when it's all said and done, to keep the final mix under control.
With judicious use of compression and EQ, you can increase the perceived loudness, without high peaks and clipping.
Set your master bus volume to 0. This tells you what the levels are in the project as a whole, but don't worry too much about it while tracking.
Focus on your source tracks.
If these start out clean, it's much easier to keep the whole project sounding good.