Assuming you don't have USP integration set up already, go to edocs.mitel.com and get the MiCollab Installation and Maintenance Guide for MiVB for your release, and take a look at Appendix C, which walks you through the setup for an existing MiVB and MiCollab server. Then for setting up the users, you'll need to configure emails and login ID's for all the users (and optionally sync the users with AD if you want to save them from remembering another password). Also do the work of setting up your feature profiles and user profiles on the front end, it will save you headaches later. Also get your roles and templates set up to make adding new users easier.
As far as Teams integration, Mitel Assistant works, but doesn't really have any features to speak of. You can't even add a speed dial directly, it has to come from either the global address book or the user's Outlook contacts. It's been a couple years since I played around with Call2teams, but I remember that was pretty limited as well.
