Best of luck!
The ATEM models do seem to be great, especially considering the historic price of such things (which every review painstakingly explains to you at the start) but they do seem to be very "industry". ie, the answer to every question is to build a TV station and hire an army of people to do everything manually in the same way it was done in the 1980s. This is similar to when I ask a question to any pro who works in the studio system and their answer is to shoot my home videos how a studio shoots a feature film.
When I look at the ATEM device, I see a few buttons that do a single thing, and a few buttons that run some hard-coded macros. Why there aren't buttons to run the user-defined macros until you buy the $1000 Extreme model is silly - the Mini has buttons I won't need, let alone the 500 buttons on the Extreme. What you really need are a few buttons where you can store and then recall configurations, so you can have Config 1 with HDMI 1 (showing yourself), and Config 2 with custom PiP settings (showing your slides with you in PiP with custom location etc), etc, then you could swap back and forth without having to punch a bunch of buttons each time to re-create the settings while also looking professional in front of your audience. The saving grace is that in the default setup you can swap from HDMI 1 (you) to HDM1 2 (the presentation) without looking, and then when you have to look down at the ATEM to find the stupid PiP button at least they can't see you fumbling around because you aren't currently visible.
It's typical BM though. Like with the Speed Editor - the middle and largest section of the controller is for multi-cam only and can't be configured to do anything else.
Anyway, rant over.
Using an iPad to run the slides seems like an elegant solution.
I find that when you're presenting to a group, you need two main things:
To see what you're sharing to the group
To see the people in the group
For my day job I do this using MS Teams (the platform chosen by corporate) and having a triple monitor setup where I have the meeting on one screen and I share another screen, so I can just drag any window I want onto that monitor and it's shared. I share a lot of different things like Word documents, Excel sheets, web content, as well as Powerpoint, etc. Oddly, Powerpoint tries to be "smart" with Teams, and when you're in Teams and hit the Present button in Powerpoint they try to be clever and talk to each other but just screw everything up.
My wife is just getting setup and her business hasn't gone live yet, but she'll be using Powerpoint and Zoom with a USB webcam, which our early tests show is a similar situation with them trying to be clever but screwing it up. I suspect the eventual setup will be a real camera and a laptop running Powerpoint going into the ATEM, then that plugged via USB into a second laptop that is running Zoom and controlling the call. The goal is to be able to fit the whole setup in a suitcase for travel, including camera / tripod / switcher / lights / stands / diffusers / etc, so we can operate from anywhere. The laptops would fly carry-on of course.