Derailleurs can last a LOOOONG time. Brakes too. Bottom brackets too. Headsets too. Shifters too. Hubs too. Rims too. Almost indefinitely. Consumables are brake pads, chains, cassettes, chainrings and tires. Even those can last several thousand miles. I am sure I overlooked something. But the bottom line is that yo aren't likely to have to upgrade anything for quite some time unless you crank out major mileage. Welcome to the forum and the joys of life on two wheels.