[2ndgen]

You can bleed the ABS if you have alfaobd and an OBD dongle, will let you cycle the ABS pump.
I haven't done it on the Nitro, but for my other Dodge it has an "ABS bleed procedure" that you just start and it cycles the pump then directs you to go bleed RF, then it cycles the pump, then tells you to go bleed the RR, then it cycles the pump, then you go bleed all 4 corners again.

 

[2ndgen]

Anyone have a diagram or drawing that shows all the pieces/parts of the entire system?

SW catalog

There's really not a lot to it:
Pedal and brake booster.
Master cylinder and reservoir.
ABS pump.
Lines.
Calipers, rotors, pads.

 

[2ndgen]

Is it possible the creaking is coming from the parking/drum brakes?

 

[2ndgen]

Pretty sure the ABS is completely inactive until it's not. I believe it should just be a complete pass-through until it engages. From what I understand you can unplug your ABS module from the wiring harness and drive just fine w/o it (you'd throw some codes), but the rest of the physical braking system would never notice.

As far as proportioning, I'm not sure how that's done--could just be done right at the MC by way of the actual physical sizing of the lines going through that point of distribution. AFAIK it's not adjustable on the Nitro.