I found another post that says SmartThings used about 100Mb so I guess Freedompop would be good for up to 5 days of outage per month.
Also, SmartThings Hub has 4 AA batteries and I found this post saying that it can last 10 hours so you don’t have to add the hub to the UPS. That would give you more time for your internet router/modem and the mini router. It would also give you a way to know there is a power outage since the mobile app would know the hub is on battery power.