There is a specific oil type for use with R143a - shouldn't be hard to find.

As for the amounts, it's difficult to know exactly how much to add.  It seems each of the component within the AC system requires a certain amount of oil.  As DLY says, it's difficult to know what has leaked out and how much to add....  I would rely on the professional AC shops or MINI dealer to figure this one out....

If you can see the air conditioning compressor, you should be able to get this information from the label. I believe these use a Sanden SD6V12 model compressor, so if you verify that, you can find the info you need online even if you can't see the compressor in the engine bay.

However, there is no way of knowing how much oil is left in your compressor and system. There is no oil level gauge or sight glass. The only way to reliably know how much oil is in the compressor - A/C system is to remove the compressor and drain it. Usually the dryer should be replaced as well, since if the compressor was damaged, oil may have leaked into the refrigerant loop and accumulated in the dryer assembly. Even if your compressor has a plug to put in a oil dipstick, you can only do this after the system has been drained of refrigerant.

Other than that, it's purely guesswork. Too much oil is bad too, but if a lot has drained out you already are at risk of compressor damage. You'll have to guess how much to add.

Hi Need some guidance here. 
Due to leak in condenser AC system was empty with some oil leakage as well. I have replaced condenser filled R134a but don't know how much oil has drained. 
What kind of oil I should use and how much? Under the hood label only says R134a and its volume . No mention of compressor oil. 
I appreciate your help and thanks in advance.