Is Particle's mesh and BLE suited for this use case?

[shanevanj]

Let me try and answer so of this

@NiSt

Would the mesh still persist when the devices are offline but still powered on

Yes

@NiSt

What happens in the event all devices are down/out of power and are later powered on–would the mesh still persist then?

Yes (credentials are stored on the devices that will allow the resumption of the mesh)

@NiSt

Is it possible to expand the mesh using BLE in conjunction with it?

AFAIK - Not at this point

@NiSt

What are the current upper limits on the number of mesh ...

This thread has lots if interesting info about testing with large meshes - a common observation is that in a large (>10) mesh the end nodes (xenon in your case) should be sleepy (connect infrequently and send data and disconnect.) this is so that the total mesh bandwidth does not get congested.

Large Mesh Networks Thread

I have shared this in another thread, but figured it was worth sharing as a separate thread to see what others are doing. I now have a 56 Xenon mesh network running without any issues. 55 edge devices 1 gateway with an ethernet bridge connected to a Raspberry Pi over USB & Ethernet. If anyone has other large networks, I’m interested to hear about your setup and what you’ve seen so far.

This https://docs.particle.io/reference/device-os/firmware/xenon/#bluetooth-le-ble- has the best information re BLE - limits are listed at the end of the section linked above.