I'd work on getting the codes taken care of first then places gauges on the suction and discharge to determine if the system has enough charge.

These cars use a variable displacement compressor so pressures don't act like a compressor that is cycled. One of the pressures remains stable and the compressor varies volume as cooling loads change. I don't recall for sure if the suction or discharge remain stable, pretty sure it is the discharge side.

Next comes trying to find the leak, sometimes this is very difficult. I've gone so far as to clamp AC hoses shut to split the system up then watch for pressure drop. At least this way I have an area to concentrate on.

You will need a scale accurate to 1 ounce to assure proper amount of when recharging.