I do a fair amount of tracking of bands, live orchestra and big band recordings and the like, with up to 24 tracks at a time. When in a studio situation such as you describe, I much prefer to work with software monitoring off and rely on the "almost zero latency" advantages of the metric halo MIO console. Having said that, any tests I ran tracking up to 16 24 bit 88.2 kHz at 64 bit were just fine. I am also running an 8 core mac pro.
When tracking with software monitoring off, I do tend to leave the buffer I/O setting somewhat higer, usually at 256. Low latency monitoring is for me important when overdubbing or tracking virtual instruments, or having a guitarist playing through GAP, GTR etc.
What you should definitely do is test your whole system thoroughly before a paying session starts. Simulate everything you will be doing - try to get some musicians who are prepared to be guinea pigs to play for you, set up their monitoring, make sure they are compfortable and last but not least, listen to the recordings and make sure they are free of any clicks or other glitches. These days, native DAW systems are capable of so much, but they still remain complicated beasts 🙂
HTH, kind regards
Mark