Check the specs.
Dream Machine is a Switch, a Router, an Access Point, a Controller but no NVR.
The dream machine pro is the a pro version of it that also has NVR but doesn’t have a built-in Access Point, but much much powerful with more capacity and it might be upgradeable and more serviceable (haven’t checked on these, you’ll need to confirm).
The Google WiFi is a switch, router and access point.
If you want separate devices you’ll have to get a router, a switch, an access point and the Cloud Key Plus (which is the NVR and Controller).
The Dream Machine Pro is overkill but it has the NVR.
Neither one of the Dream Machine versions have PoE.
You can just buy the switch (don’t see why would want the switch unless you want the PoE feature) and the Cloud Key Plus (which is the controller and NVR), I think you could even just use the Cloud Key Plus with the cameras.
But it seems the price of the Cloud Key Plus is kinda obscene you might as well top up a little bit more and go with the Dream Machine which will grant you a big bump in network performance, capacity, features.
If you get Dream Machine Pro you can use a standard consumer router as an Access Point so you don’t have to get one. But in the case of Google WiFi I’m not sure if it can be used as an AP you’d need to check on that, they’re fairly basic and featureless devices that just works but don’t give you much control or features… since you’re going Unifi is recommend you one of their AP, they’re so much better than Google WiFi and it integrates with the controller. You can also have a mesh network with their AP, the coverage and speed is so much better. I’m using the AC LR, that thing is cheap and has huge range. The antenna is tuned for small and low powered devices like phones, smart plugs, tablets, etc which is a huge advantage as many times these devices can receive data transmission from the router but cannot send data back due to their small and low powered antennas. This might happen to you on public WiFi where you have signal and can received it but whatever data you transmit back is unable to reach router or the router is unable to pick the weak signals.
So whatever suits your budget best, you can just buy the Cloud Key and Cameras (which would be like any other NVR system) and you’re good to go.
Here’s the component for the NVR:
You’ll need to check how these integrate with HA and the capabilities.
But beware the Cloud Key Plus is 199USD retail price and the dream machine pro is like 379USD but has so many more features that neatly Integrate with HomeAssistant and will make your network so much better, the cloud key alone is kind of a rip-off.
Anyway you’ll grow into the network stuff that requires a proper router and a not a featureless Google WiFi.
For example we’ve been discussing all the stuff you can do with Cloudflare and a proper router on this thread: