Any private key which produces a public key, which when hashed with SHA-256 then RIPEMD-160 produces the above number, would be able to spend coins at that address.
I didn't say the opposite. I said it may. It may also have none, it's just extremely unlikely.
Minor correction: If you have 4 possibilities for one character in a 64 character private key, then the total number of possibilities is 2254. If you knew for certain one character in the key, then you would have 2252 possibilities.
Why do you have 4 possibilities for one character? Isn't it 16? (0-F). I don't get this.
Actually this needs a correction:
(for every hex character you remove you have 24 times less combinations)