You have public key, you can try and find the private key for it.
Knowing a public key reveals zero information about the associated private key, and does not make brute forcing it any easier. You still have to check 2
256 keys.
You have a (valid) private key, you can try and find other public keys for it.
If you have a valid private key, then you can find exactly 1 associated public key. I'm not sure what you mean by "find other public keys" - there are none to find.
As you say the odds are slim, but they are still odds.
Apart from time, CPU power and storage, there is nothing stopping you from generating a list of all the pairs in existence.[/quote]
Apart from time, in that the sun will die before you get even a tiny fraction of the way through, and CPU power and storage, in that even just
listing every private key (never mind calculating and storing the public keys or addresses) would take up approximately 1 billion trillion trillion trillion
trillion (10
57) more storage than there is in the entire world.