In all honesty 2 would suit me better unless you are really on a time crunch, as you want to be able to take a good run at the beginning research etc, and this is generally the time to do it.
The explanation of this I'm taking directly from "User Experience Team of One" by Leah Buley.
"A persona is a composite picture of a collection of users boiled down into one relatable, human profile. A persona is usually presented as an individual person with a name, a face, and a backstory. Personas usually explain that person’s needs, values, goals, frustrations, and desires. Personas are made as human as possible to further enhance the sense that this is a real person with a messy life and quirky ways of coping with very recognizable human situations. A persona is a fictitious composite based on extensive user research that you or someone else has observed firsthand. The trouble is, creating good personas takes time and resources.
Proto-personas are a modified version of personas that stimulate the same type of empathetic and user-oriented thinking, but with less investment in time. They can be created with the help of the cross-functional team, which makes them a quick and inclusive tool for turning on the user experience goggles. In essence, proto-personas are a persona hack that you create using whatever data you have available and with the help of the team. Whereas a classic persona is based on firsthand user research, a proto-persona is based on whatever insights you have, which can include secondhand research, or even the well-informed hunches of a team of people. (Of course, if you have firsthand research to refer to, that’s ideal.) Proto-personas are less scientific and rigorous than traditional personas, but they can be equally effective for helping a team shift into a more empathetic mindset about users’ needs."
I think what you would be looking to create is personas, as we have actual people that we can talk to to at least have a basis for them :).
So I've already got 3 Senior UX designers, and 2 HR staff that are happy for me to interview, so I'll do that next week if I get the go ahead from you. It would be a good exercise too for us to come up with questions to ask them, and validate it as a group too. If we have a common set of questions and a format, then others can also do some face to face interviews if they have willing participants, and that can give others some interview experience.