I was thinking about using Pi's for some cameras, but your readme says something about using a Google firebase for passing messages... would email to sms make more sense (if your provider still supports it)?
Also, if I were to set this up behind a firewall, would I need to port forward something so I can access it on the road?
Using Pi's to run the hub is technically feasible (and I do plan on trying it on my end). Port forwarding is not needed. The Pi only needs to be able to initiate a connection to the server.
Google FCM is used for delivering notifications to the app. The server asks FCM to do so when needed.
Also, if I were to set this up behind a firewall, would I need to port forward something so I can access it on the road?