All your assumptions are correct and you know more than most about the wiring. The green wire for the dash lights is fed by the orange wire to the HL switch which also lights the parking lights. Before it powers the green wire, the power passes through the headlight rheostat which is the dim to bright for the instrument lights.
Simple troubleshooting for the instrument panel lights is to jump power to the green wire side of the PNL lts fuse and see if the lights come on. If they do then the problem is between the fuse and the headlight switch, either an open in the green wire or the HL switch. I would spin the HL knob a few time and see if it wasn't just light corrosion and maybe they would come on.
Good Luck.
I have a diagram of the AC circuit if you think it might help your AC problem.
BTW welcome to the forum.