Holden Commodore Problems

It sounds like it could be a problem with the brake master cylinder. Take it to a brake specialist who should be able to sort it out for you.

Running the higher pressure shouldn't have any great effect on the wear of your tyres as you describe, but you could drip it back to the specified pressure and see if that makes any difference. I would believe that what you are seeing is the result of the alignment Holden uses.

It sounds like an electrical problem, but being intermittent it can be hard to trace, as you have discovered. I would be checking the crank angle sensor and its connections.

It doesn't seem to be a major problem, so it could be that it needs a tune-up. Perhaps fit new spark plugs, clean the throttle body and the injectors.

It's suffering from fuel surge, and I would be looking into the fuel tank, to the anti-surge fuel pot.

As it's not a consistent problem you would have to think there's an issue such as a connection or a sensor that's faulty. The factory system used by Holden is an Impco one, designed and developed by Impco for Holden. I would bypass the Holden dealer and go to an accredited Impco dealer and have them check it for you.
 

Change the oil before you drive it as metal particles can lead to severe engine damage. Talk to the dealer and demand it be fixed under the warranty.

It's a service reminder and should have been reset by the mechanic at the time of the service. Take it to a Holden dealer who should be able to do it for you.

It is unusual that the airbag required replacing so soon, but the car is going on for eight years old and, as Holden said, the warranty expired some time ago. Where it was serviced wouldn't have had any influence on the failure, what Holden was telling you was that because you hadn't had it serviced at one of their dealers they would not consider a goodwill payment.

That's what happens when you change to low-profile tyres and fit harder springs, shock absorbers and bushes. You can try different shock absorbers, which might help, but there's not a lot you can do about it.