I made my way to the Gravitee and it was only 1 :(
I'm afraid to start a mine in the aether I don't want to accidentally fall through.
Just don't dig directly beneath you. Just like the rules of normal world mining.
This brings up a question: What do we call the "normal world" in Minecraft? The Nether is below, the Aether is above, but what's the main middle part called? It's not quite "Earth"...