For bit depth, I think the main thing is you're better off recording at 24-bit (and we're talking about the audio interface's actual converters) for headroom when adding effects, etc. If you then export to 16 bit for CD Sonar will just discard any extra bits without having to recalculate.
For sample rate it's best to either record at the same sample rate as your final delivery medium (i.e., 44 for CD, 48 for DVD) or a rate that is evenly divisible by the rate of your final medium (88 for CD, 96 or 192 for DVD). That way Sonar either won't have to recalculate the sample rate at all when exporting, or it will be an easy calculation. If your final medium will only be MP3, then you have the choice of either 44 or 48, so just try to avoid recalculations when Sonar exports.