I don't think computers, with all those fans and spinning hard drives,
would be suitable in a silent audio room... Maybe a fanless power
supply in a diskless machine operating as a terminal to a "real pc" or
something similar.

Regarding fans, the front intake fans are best for cooling hard drives
in their airflow - high-speed drives get too hot to touch when tucked
away from the airflow, which is never good. The fans were not plugged
in either by mistake or intentionally so that you would decide the
noise vs. cooling or plug them in as you add new components to the
machine.

You can get a single cable combining keyboard, mouse and monitor. A KVM
cable would probably be ok but it must be male-to-female (male to PC,
female for the devices themselves)