That's old JLG terminology. There are basically two types of controls, proportional and bang bang. Proportional is the drive, boom up/dwn, and swing, those operations are proportional to the degree the control lever is moved. Bang Bang describes functions that work with toggle switches, bang on, bang off, it's just an old JLG term for toggle switch controlled functions and valves.
True, but not entirely with proportional solenoid valves, they work with Pulse Width Modulation (PWM), and some PWM coils don't work with full 12V so if you put 12V on them to check magnetism it will fry them. I don't think the proportion coils on these machines are less than 12V, just saying one needs to be careful putting full system voltage on a PWM coil, that's all.
Drive fwd/rev works from a different (hydrostat) pump than all other functions of the machine. Boom up/down and boom swing work from a gear pump feeding P1 port on main control valve, all other functions work from another gear pump that feeds P2 on main control valve.
Yes, you're reading your diagram correctly. When you posted earlier that you verified the main dump valve was working because other functions that use the dump valve work. I thought "what, his steering works?", to which I was going to ask but you beat me to it to confirm. Ok, knowing this, I'm going to have to do some more noodling in my head. None of your toggle switch functions work from platform or ground, but your steering works, correct?