Switching from external email host to Office 365, I have some questions

So I've been pushing to switch from using out ISP as our email provider to using Office 365 and with recent developments it's looking like it's a possibility but I have a few things I need to figure out before I get to that point.

I already know I'm going to have to use some PowerShell commands as well as a lot of .csv edits to get contacts into the system, and I'll have to do the same for the .pst files for each of them as well. I already have tried it in the past and it seemed to have worked well enough so I'm not too concerned about that.

However, something I am concerned about is some of the accounts I have created on Active Directory, shared login accounts.

Currently we have an email address data@example.com. We have two users that manage that data@example.com email address through the Data user on Active Directory.

The way these two users operate is one mainly remotes into the desktop set aside for Data to manage it and the other remotes into it as well (usually kicking them off) to work. Obviously this isn't ideal but it's the setup we have.

If/When we switch over to Office 365 I want to turn the data@example.com into a shared mailbox and remove the user completely. My main concern is what will happen to those old data@example.com email addresses? Will they be able to be transferred into the data@example.com mailbox if it's a shared mailbox?

I do have loads of other questions about it but right now that is my main concern.