That's the thing about black holes that always blows my mind. I don't understand how the larger a black hole is, the less dense that it is. In my mind, I always think of black holes as super dense objects containing so much matter in such a little space that the gravity is crazy strong. How can something so not dense be a black hole? It doesn't make sense to me!
To be fair, the density is calculated from the event horizon, which is a somewhat arbitrary boundary. All the mass is still concentrated at the singularity which is still infinitely dense, just... a bit more so.
Not really. If more material falls in, its mass and size increases (the volume increases faster than the mass, which is why it's so unexpectedly low density in the first place), but otherwise it just sort of sits there.
Over the very long term, it will evaporate away by Hawking radiation. But that's a very very slow process. Like, long after everything else in the universe has ended.
For lay people it's a point in space. If you want to go into general relativity and explain to people the weird geometry inside of a black hole and all the math that goes along with that go for it.
But all that doesn't matter as this picture is still representing the event horizon and not the naked singularity.