Regarding compressed/ uncompressed addresses, why does directory.io list compressed addresses next to uncompressed ones? When you create a compressed address is this in fact a new address from the 2^160 pool of public keys?
There is no pool of 2^160 public keys. It is a pool of 2^160 addresses, not public keys. There are 2^256 private keys and each private key has exactly one public key, so 2^256 public keys. Each public key can be represented in two ways, in uncompressed form and in compressed form, so there are 2^257 representations of all public keys. Each representation of a public key corresponds to exactly one address because it is a hash of a representation of a public key. Because of the pigeonhole principle, more than one public key can correspond to the same address (and thus an address can have more than one corresponding private key).