First, you need to know what refrigerant will be used in the system....r12 or r134. This will determine what oil you'll use. Are you doing a conversion from r12 to r134 at this time?....if so, you need to flush the system....r12 oil will be a problem in a r134 system.
How much oil to put in depends on how much was lost. Without flushing all the plumbing, it's only a guess how much needs to go in. Assuming the compressor you got was sold without any oil, a compressor change requires replacement of approximately half the specified oil charge (you'll need to find the specs). It can be poured directly into the system before closing it up (recommended), or charged from pressurized cans after it is closed up.
You didn't mention anything about the dryer/accumulator. This should probably be changed along with the compressor. Moisture in the system will eventually form acids that shorten the life of your a/c system.
Did your old compressor break up internally, sending debris through the system? If this happened, you need to flush out the debris from all the components or the new compressor will fail in short order.
95 E320 Cabriolet, 131K