bushytails

A bottle of Lucas can help with startup noises, although I haven't tried it on that exact engine.

If it's 5 years old, it's probably just time for a new battery, as long as it's reading >14V with the engine running, showing the alternator is good. You can try using a non-automatic charger - one with no blinky lights or any intelligence - to un-sulfate it, by disconnecting the battery from the car and leaving it on the charger for several days. You want the car disconnected because you're trying to intentionally overcharge the battery, and don't want the car seeing high voltage. An automatic charger won't work. Has to be one that's just a transformer, rectifier, and meter.

I think you're posted in the wrong section, so you might get fewer views. I don't know where to find that specific switch, but they're fairly generic - just find one with the same thread and function, or get a new binary or trinary switch. Have you confirmed the switch is bad? They don't fail very often. I assume it's staying open even when your manifold gauges show correct pressures, and jumpering it kicks the compressor on?

That's an aftermarket anti-theft module that takes a "key" that's a little flat thing that looks like it goes to a treadmill or something. The correct repair, as you already found, is to toss it in the bin and put the wiring back to stock.

Late reply, but old gen oem oil pressure senders are bimetal type, and can't be read with a meter. Aftermarket rheostat type sending units can be read with a meter. If you have the factory sending unit, you'll need a compatible working dash gauge, or to use a mechanical gauge for testing.