When configuring actions for your devices and monitors, you should take a few things into consideration.
Imagine the number of messages sent if external notifications are placed on a router and every device and monitor that uses that router for their connection to the Internet. If the router goes down, it will appear as if all of the devices are down, and messages will be sent for each of them. Consider using dependencies and limiting the external notifications to the router and the most important of the devices in the group.
Sound notifications are safe to use in almost any situation, but is not the best choice for items that are monitored overnight.
You may want to add device states for longer periods of downtime. Perhaps creating a Down at least 60 mins state, and sending an escalated message to show that the device is still down after an hour.
Whenever possible, it is a good idea to use action policies over actions configured for a single device. That way, you can reuse the work you put into the list, and can keep better watch over the actions that are being fired.
Unless the device is vital to the daily-operation of the business or office, the state change color and shape should be enough to let you know what is going on with your monitored devices.