@Drew Perkins Miro states there is a video limit of 25 participants per board - more on that here. With this in mind, you may want to split the group's into their own boards.

I have also heard rumors of Miro-Zoom integrations, but have not used any get. Here's one community post about this.

Thanks, I’m new to Miro but there’s an embedded video chat feature right? Would that not work? Or are you saying the video chat limit is 25 per board?

The 25 participant limit is for Miro’s built-in video chat feature. As for embedding any 3rd party video chats, I cannot speak to that. What I have heard from others is that it would probably be easiest to use Zoom to host all of your participants for video/audio and then Zoom’s Breakout Rooms for your 10-15 person working groups. As the facilitator, you could either share your screen (your Miro board) on Zoom or use Miro’s board Screen Sharing as you lead the participants through the session.

Honestly, using Zoom for the video/audio would probably cause less headaches when working with such a large group of people as using Miro’s video/audio chat make cause more confusion as each person’s needs to set their camera/mic preferences in their OS or browser, but that’s just my personal opinion as I found the user experience to be less friendly than video conferencing applications which provide an interface to your camera/mic settings.

Thanks, we’ll probably use Google Meet and create multiple rooms and they could just open Miro in another tab or window and use the ongoing audio from the Meet session in the background. I do need to know if there is a limit to the number of Miro boards I can have going simultaneously and whether I need to be in all of them. I’m anticipating providing links to the various boards and Google Meet rooms I’ve created, having them go there and collaborate and I could jump in and out to check progress and/or answer questions. 

I don’t believe Miro is going to limit the number of board connections by IP address, so you’d probably only be limited by any external factors - Internet bandwidth, computer/ browser memory, etc. Personally, I have found that my Chrome browser (on a decent quality laptop with Windows 10) can slowdown when I have some large Miro boards open, along with a number of other sites on other browser tabs. I have found myself using the Miro desktop app more and more these days which opens each board in its own tab by default. You can download their apps here. Note that the Miro app in the Microsoft Store is not the same as the one in the link I just provided (it does not have the exact same functionality).