I will try to answer your questions.
O2 sensors will set a fault code when they begin to fail (slow response) or fail (no signal). I wait until they set these codes to replace. On one of my family's E39s two of the sensors set slow response codes at 164K miles and I replaced them all so I did not have to do the job 4 times, one at a time. They had worked fine IMO. Many change these sensors at 90K or some other mileage but mine worked fine until the car told me they were not.
The DISA valve can start falling apart and you will also get a code telling you that there is a problem. Partiular to your engine, a M54, the metal pin that holds the flapper can work its way loose and when the frame that holds the flapper breaks the pin can get sucked into the engine and cause damage. This is a rare occurrence but there is a kit to fix the problem. You'll have to search for the kit as my cars have the m52TU motor which does not have this problem very much. I superglued my pin into place. The DISA can also leak around the o-ring. BMP Design is the only place that sells a replacement o-ring.
A properly performed smoke test will reveal any vacuum leaks but the person doing the test has to know the car and how to do the test. As helmet75 said, it may take a while, 5-10 minutes, for the smoke to reach deep into the intake and associated sustems. As I said, the mechanic doing the test has to know what he's doing and have patience. My smoke machine, a Smoke Pro, has a gauge that tells you if there is a leak. So if the gauge indicates a leak, you have to be patient and wait until the smoke appears.
There is really no specific test for the CVV but many remove the oil fill cap while the engine is running and if there is a huge amount of vacuum there, the CVV is shot. There should be some vacuum at the cap but not a huge amount. Another sign of a failed CVV is a plume of white smoke out the exhaust at startup. A search on this forum will tell you about a failing CVV. Using the Wiki section ( top tool bar at the extreme right) will provide much info.
You MAF is fine showing 13kg/hour. Tihis value is not absolute and will change with air temp and elevation above sea level but yours is in the neighborhood. Another test is to measure the voltage at the signal wire-should be between .5 and 4.5 volts depending on engine speed. The lower value is the idle value. Different engines have a different number of wires so you will have to search for your car. Mine has 3 wires and the yellow wire is the signal wire-yours may be similar but I don't know. Take a look.
Live data will have many readings that include coolant temp, intake air temp, short and long term fuel trim for all 4 sensors (both after CAT sensors basically watch the CATs for proper operation and have only a very small input into how the engine computer adjusts air, fuel and spark), the voltage being generated by each sensor (if you graphed these voltage readings, you'd get a bell curve approximately), short term fuel trims tell you what the engine is doing NOW, long term trims are much more stable as they are a sort of average of the short term trims over time. The volume of air flowing thru the MAF is also reported. Hopefully, the MAF is correct. I've made a table for my car with a known good MAF showing the volume, ambient air temp and elevation for different rpms up to about 3K. Very useful for checking on the MAF. I can't remember exactly but any short term fuel trim (all fuel trims are displayed as a percentage) that is either plus or minus over 10% for over 10 seconds will set a code.
I think that experience with live data is the best teacher. The fault codes point a finger at the problem and you have to have knowledge of how everything works to interpret data and solve problems. Research and reading is the best teacher or take some classes at an automotive school. A friend of mine who is an excellent tech says he doesn't have to get dirty diagnosing problems anymore because Google knows all.
I am no expert but just a DIYer who has been working on his own cars for many years. I did work in a repair shop as a service manager for 8 years and learned a tremendous amount during that time.
