I will answer part of your question. The main circuit of a passive preamp typically does not require a power supply. So no AC power required. In some cases, such as those using Light Dependent Resistors a power supply and AC power is required. You may also require power if your passive features remote control volume like the Placette RVC and no longer available Bent Tap (although I think you can still get the DIY remote kit). The idea and one of the main attractions of a passive is simplicity and to act just as an attenuators and possibly input switcher.
Now for the rest of your question spend the next several days reading this thread and I think all your questions will be answered:
Lightspeed Attenuator - Best preamp ever?
Now for the rest of your question spend the next several days reading this thread and I think all your questions will be answered:
Lightspeed Attenuator - Best preamp ever?