Regarding fuel pump wearing out and allowing fuel back in the tank. You can test it by turning ignition on/off couple of times for several seconds before You start engine, this will allow fuel pressure to build up and engine will start straight away. But that could also mean leaking fuel pressure regulator. Or You could undo fuel hose going to the injector rail next day after car have been standing and see how much if any pressure remain there.
But this is all just guesswork You really should get it diagnosed on PC. If there is intermittent problem with sensors it will show up as fault and You can check for air leaks by looking at measuring blocks from MAF, knock sensors, engine load , O2 sensors and injection times.
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