> Auto-restart the reverse-proxy if bandwidth usage drops to zero for more than 2 minutes
It's understandable in your case as you have traffic coming in constantly, but first thing that came to my mind is a loop of contant reboots - again, very unlikely in your case. Sometimes such blanket rules hit me due to most unexpected reasons, like the proxy somehow failed to start serving traffic in the given timeframe.
Though I completely appreciate and agree with the 'ship now something that works now' approach!
What are you using for email? It seems like Sendgrid/Mailgun bill would ramp up quickly with a large userbase.