Can you isolate the intended instrument or voice for each mic input?
NO. There is no practical way of doing this. This is the "holy grail" of audio processing that people have been pursuing for decades without success.
Can you predict the levels from different microphones in some attempt to "automate" the setup?
NO. Especially in transient setups (different venues, different acoustics, different physical configurations, etc. etc. etc.) There are millions of variations which make this an impossible task on a practical basis.
Can you use multi-track recordings to "simulate" performance as an aid for sound-system setup and initial level settings?
YES There are several simple multi-track recorders that can be plugged into the "effects loop" of a mixing desk. They can record ALL the channels of a performance, and then they can be used to play back ALL the channels in the same levels as the performance. That way the sound people can do a first-pass equalization and mix settings before the performers are avilable for a proper sound-check.
Some of the recorders that have been made specifically for this process include products from JoeCo, and Cymatic Audio.