Complete A/C rebuild Q

This might be quite a read but here goes.

I believe I have bought all of the components to rebuild the stock A/C in my 73 duster:
compressor rebuild kit - (not sure if i need it yet as the comp still spins)
Dryer.
Expansion valve.
O rings.
Retro-fit kit with correct fittings for year.

The system is completely empty.
I have done a conversion on a late 80's ford with good results but not so sure about this old girl.

The questions start here:
The expansion valve has a sensor that connects into one of the lines.
Should the sensor be soldered into the line? (when I took it out it looked like it just had grease on it or oil and just slid out no seal or anything. so how does it hold pressure?)
The dryer does have a pressure sensor on the front of it.

And the low pressure port is the one on the top of the comp or the one on the fat line?
I'm hoping that the guy before me just didn't know what he was doing.

I plan on replacing the parts myself and having a shop do the vacuum/pressure test and I'll recharge. (that's what i did on the ford)