1. Yes, the same app can operate multiple OGs. If you use the Blynk app, you can scan the OpenGarage Blynk QR code three times to create three projects, and you can give each a different name so it’s easy to remember. If you use the OpenGarage mobile app, it also supports adding multiple controllers. In either case, you can switch between different controllers within the app.
2. Notification is only supported by the Blynk app — the notification message does include the device name, so as long as each device has a unique name (this can be configured on the controller’s settings page), then you can easily tell which notification is from which controller.
3. I am not sure what type of automatic gate you have, and also how you intend to use OpenGarage with it. You can think of OpenGarage as a WiFi-enabled door button — it can sense the door status, and you can trigger actions remotely. On top of that, you can enable automation so that it auto-closes the door if it senses the door is left open for longer than a specified threshold. If your automatic door already does the closing on its own, then you can just leave OpenGarage automation disabled so they won’t both try to control the door at the same time.