Haha yes sordid. Thanks. That’s not a word i have ever used. :).
“deliver my soul upon the subject” means to tell someone intimate/personal details that you usually wouldn’t tell someone. “which made him the last man with whom one would care to take anything approaching to a liberty” means that since Sherlock is so nonchalant he is the last person he would want to offend. This is an archaic form of English from England even I a native speaker had a hard time understanding what it said. But basically “take anything approaching to a liberty” is intended to mean speak your mind or say something that might offend. Hope this clears things up.
Nice retrieval on the source, Caldazar. You are right: Absolutely nobody speaks like this today. Cheers!