Hi Brian,
I think it depends of the "flavor" you want to add to your recordings. Most of todays mixers are transparent in that they offer or add no color to the mix. I am old school and old to enough to be able to recognize the specific character imparted by say a Trident, MCI or API console. Same with microphones. SO what you are asking depends -
Typically, I can record 16 tracks at once and playback the same number of channels while recording. Neither Sonar nor the PC has any trouble handling that.
I often have songs with 60, 70 or more tracks so I use stems. That means certain things are sub mixed in Sonar. Say drums. Even though I record KICK, SNARE, L&R TOMS and L&R OVERHEADS, all of those tracks are sent to a DRUM buss in Sonar and that is always outputted to channels 1&2 on the TOFT console. You will be surprised how efficient it can be to send out stems for further processing in a mixer and external hardware.
The key thing, in my mind, is to figure out the SOUND CHARACTER that you want your studio in have. Different hardware will impart different character. Different plugs can too. I love UAD plugs and use dozens of them in every project.
I don't know if I am helping or not, but you have asked complex and highly personal taste type questions.
I do not use the MASTER buss in Sonar because of the way I work. When I mix, I send the signal from the Toft to both the Tascam CD burner and the Otari 1/4" tape machine at the same time. On those mixes I now have "printed" or imparted the wonderful sound of the console and if need to, I can always re input the CD or tape playback back into the PC. But I never do.
I do not attempt to master the mixes here. They are always sent out to a mastering house. Those guys are the real audiophiles and have speaker systems that cost a much as a car. It is important to me to have that additional set of critical ears listen. If something is wrong -they will catch it.
But you specifically say gear to record and "CONTROL multiple tracks so that implies a mixer/control surface. I also have here in the studio a Tascam DM24 which has the 24 channel I/O IF/FW card installed. Although I am not using it everyday because I am currently patched to the analog Toft ATB 32, the Tascam digital mixer is absolutely awesome. Fantastic as a controller. Stunning clarity and stereo width too. But it is a steep learning curve to get into it really deep. As with all digital mixers, it is the LAYER format and can be quite confusing to the new user but the format will become very intuitive with use.