Sounds like a very practical project! We use a lot of motion-triggered lighting at our house.
First, what country are you in? The device selection and even some of the app features do vary. And light switch selection in particular is very different by region.
I’m not familiar with the Nest cameras, so hopefully someone else will have ideas there.
My first thought would be just to try the cameras by setting up a dummy routine to send a notification for motion so you can get an idea if they might work.
If it seems like they won’t, my own suggestion would be to use a standalone sensor rather than one built into a switch unless it’s for a very narrow passage. This lets you place it in the best position or even combine 2 or 3 into a zone.
For example, at our house we do use an integrated switch in the utility closet. There’s no point in having a separate sensor there since the sensor built into the switch does catch every time the door opens, which is all we need.
We have a large living room, though, and that switch is near the entry. Works fine to catch someone going into the room, but they are invisible to the switch if they come in from the patio or are sitting on the couch,. So we use multiple standalone sensors in that room.
So little details can make a big difference for each location.