"unlimited data" seems to be "1.5 g down", so double check your offer.
Hotspots are great devices though, just a little pricey, but could be OK for professional use.
They have a limited range too, did you plan on having one per camera?

Start your project step by step. You mentioned solar, so make sure you have solar panels and batteries installed and working before you can connect cameras to it. Devices such as Raspberry Pis with a camera and infrared light attached are probably cheaper than IP cameras, and more versatile too. You could for instance store the camera feed locally and send you only snapshots at a regular interval or in case of events like intrusion, with a different alert level. The regular camera feed could get uploaded to a local storage pending retrieval. A Raspberry Pi is a small computer and can be programmed to do anything you want, it's perfect for such remote sensor usage. You just need to find yourself a trustable teenage nerd to do the programming! ;)

When I started computers 30 years ago, I could see the potential of home electronics for things such as security, energy and time and effort savings, and entertainment. There was this promising I²C bus that was used to carry several signal on the same wire, something much better than the 9 or 25 pin serial connectors of computers at the time, and which were perfect for wireless signals too. Some HiFi systems used I²C to connect different HiFi modules together wirelessly later. 30 years later, and there's still no home electronics modules you can easily buy and add to a PC, and they all communicate together in the same standard format so that any vendor can create a new weatherstation or different types of alarm/intrusion detectors, or garden watering system, and the same open source home automation software would handle all this transparently. I even saw last year or so an announcement, I think by Intel, that one of its chipsets or something would support I²C. 30 years later...