Ok, I'll take a stab at this.
Ford, back in the good ol' days, used automatic transmission fluid as their power steering fluid for many reasons. My '88 B 600 uses it too. So the guy from O'Reily's is correct for this particular year. ATF fluid for an '84 Ford whatever will always work for your application.
The air compressor is oiled from the engine oil. You can verify this by looking at the air compressor and finding a small steel tube coming from the engine going to the air compressor. This is the oil tube for the air compressor. It is cooled both by this oil and the air around the compressor. Looking again at the compressor we will see steel fins that are connected to the compressor cylinder. These fins are heat sinks for the air compressor to help dissipate heat from the compressor. The bottom of the compressor allows the oil that is now hot to dump back into the engine to be cooled in the oil pan and pumped back into the engine to repeat the process all over again.
As far as the air dryer is concerned, it's very rare for those to go out. It's usually a stand-alone piece with very few parts to worry about.
As far as what to watch out for if the compressor wears out? Abnormal noises just like in any other internal combustion engine. However, since the compressor does not combust fuel in the pressure chamber, timing and other issues concerning the fuel burning process do not apply. Unusual knocks and rattles are the big signs of trouble.
Hope this helps.
Firearms stand next in importance to the Constitution itself. They are the American people’s liberty teeth and keystone under independence. — George Washington