Etiquette for addressing people

I think Wall Street is generally a first-name basis. Even nicknames are used and/or last names in kind of a fratty way from my limited experience. Others may have different experiences. Not sure a forum based on “monkeys” generally would involved Mr.‘s and formal titles. Hey, even people here don’t have any names at all….

Normally, the more senior or unknown person would offer you his/her first name in business.
One possibility for your contact would be to sign his emails as "Thanks, Bob" i.e. - so check out how he signed the last emails.

In a f2f scenario the last name would be dropped pretty quickly as it would be unusual to call someone Mr. [Last Name] on an ongoing basis.

I address people in the industry by their first names. My thought process is this person would ideally be my future coworker. It's not like I'm talking with my friend's parents.

Bro never use Mr. or Mrs. that's weird asf. I've cold emailed heads and VPs/MDs and always have used first name. Not once have I been told to refer them as Mr. or Mrs. You're an adult now and adults can call people by their first name, except maybe in a bs academic situation. I would refer to them by their first name going forward. Best of luck

First names 

Start off with a ‘WAZZZAAAPPPPP’

don't use mr ffs  first name. 

Never use that but if you do, it is “Ms.” for females because it includes both married and unmarried

First name, especially if he signs off with his first name

I think that referring to anyone in Wall St. as Mr. /Ms. would be a bit off putting. I get a lot of networking emails (although I’m not allowed to answer them) and I’ve seen a few Mr. __ and I’m just like bruh you are doing it wrong I’m literally 2-3 years older than you… we could’ve been slamming down beers on campus a few years back. It shouldn’t be a big deal though. Although I echo the same advice as some of the previous comments have offered. After the first interaction look at how the banker signed the email and use that moving forward.

First name only. The only instance I have ever seen anyone called by their last name is in process letters or with formal Korean people (and even then, might have been due to their lack of English skills)
 

Calling people “Mr” would actually show quite negatively imo. If you want to be formal say “Dear 1st name”