32 is a short in the HAC circuit, not related to the turbo. I don't recall you Mentioning this previously. It's not shown in the 89+ TEWD because in the later model ECUs (mid89 and later) the HAC sensor was incorporated into the ECU itself. In early '89 and prior it was an external sensor mounted behind the glove box near the hinge... three wires. I think it too gets it's power from Vc as well as does the AFM... if so there's a very likely tie in. I believe both also use E2 as ground. Have you tested Vc? A short in the wiring harness or a bad ECU would account for all three related problems.
With regard to the TPS, I forgot to mention that automatic transmissions do rely on it more than manuals... in this case driving with it unplugged or damaged will probably result in even worse performance.... Which do you have?
Analog meters refresh more slowly so signals with oscillations are essentially averaged out. Reading Vf with a digital meter, for example, may show a bouncing signal which never stabilizes (say from 2.5 to 5V, back and forth and numbers in between).... with an analog meter it'll show 3.75 with only a slight flutter to the needle. Some DMMs do have a function to mimic this behavior.
The stock boost gauge is not a diagnostic tool by any means and I recommend you not expect anything more from it then you would from a 'dummy light'. The engine operates just like an N/A engine until the compressor starts spooling up; In vacuum. Until the compressor is spooling and producing enough compression to raise the manifold absolute pressure to ambient the engine remains in vacuum and any good boost gauge will reflect this.
You can test the KVAFM.... with Toyota's publication on advanced diagnostics and repair (this also covers ECU's, IIRC), a flow bench and an oscilloscope. I suppose you could test one with a leaf blower, an oscilloscope, a known good KVAFM (as reference) and the suspect KVAFM connected in series....
Yes, it's normal for the vent mode to remain lit as ling as the button is pressed. As long as the A/C switch is off (and it's LED, naturally) you're fine and barring a wiring issue the code 51 would only be caused by the TPS or a bad ECU.
Limp mode is only entered when a condition exists that the ECU believes is critical to an extreme degree. It doesn't even go into limp mode for a 'lean condition detected' error code, if memory serves correctly. Issues such as severe knock, damage to the ECU or malfunction of critical electronic components (there aren't many of there actually); I believe on the 7M-GTE an oil pressure signal of 0 at the ECU or at least a fluctuating oil pressure signal may cause it as well.... does your factory oil pressure gauge work?