2500 miles for a 10 speed chain sounds about right. As you approach that you should measure it.

As for how many chains before changing a cassette, its hard to say given that I'm changing multiple wheelsets across multiple bikes. But a cassette should last at least 3-4 times as long as a chain.

When you put on a new chain, and it skips with the old cassette, it's time for a new cassette.

As for new chainrings, I don't recall ever replacing a chainring on a road bike due to wear. Unless you're riding in real crap conditions, I'd expect in excess of 25,000 miles out of a chain ring.