The compressor in my 95 3.4 went bad and does not hold a charge. Def. leaking from the compressor.

I have a new compressor and drier ready to install. The compressor is dry and it says to dump the oil from the old compressor into a container and put that much oil into the new compressor. Well how do you know if the correct amount of oil was in the old compressor? Is there a certain minimum amount there should be? 4oz etc? I know not enough is bad, but too much isn't good either as it would affect the cooling.

Also, if I pull the system into a vacuum, will that drain all the oil I just put into the compressor?

Its been quite awhile since I did A/C work and can't quite remember.