1. It's been a while since I did mine. Not sure what "pins" you are referring to, but I put an AC system from an 88 3vze on my 88 22RE with a compressor from a mid 90's 22re. The connections on the top plate of the compressor were pointing in the wrong directions and the hoses wouldn't reach. I put the top plate of the old compressor onto the new one and everything worked perfectly.

2. Ester oil, not sure how much I used.

3. yup, you need the green HNBR o-rings for 134-A.

4. Always replace the drier when the system has been open. You're also supposed to use a vacuum pump to remove all the air (and moisture) from the system before filling it. I borrowed one from an uncle that does HVAC work. I've heard of people skipping this step, but don't know the consequences.

I'm sure someone who's done this more recently will chime in with more info.