No need to add to FB's advice to the OP, but I will add a couple precautionary notes to others dealing with possible drive train wear:

You don't need a tool to check for wear. It's a waste of money for a consumer, with the possible exception of someone who has a stable of bikes. All it takes is a ruler, which is far more accurate - one can find multiple examples on the forum where someone's gauge said the chain was worn more than it was. The fact that a tools exists does not mean it is useful for everyone. Google measure bike chain wear.

Don't depend on your eyes to detect cassette wear - it happens before even the sharpest eyes can detect it. The test is how a new chain behaves, or how the cassette works when switched to a different bike that has an unstretched chain.

Chainrings can become less efficient long before they get to the shark's fin stage, but of course it's a matter of utility vs. budget as to when you replace them.