Hi Michael. Setting up an alert such as you described should be doable, but I can only give general instructions without more details. The high-level actions you'd perform to get this working are:
1. Set up VizAlerts to run against your Tableau Server instance.
2. Take the Viz in question that you're talking about, and filter it to the time window you want to check for the threshold being exceeded. Let's say, for example you want it to "alert me if there are more than 50 transactions over the last hour". Filter using a relative date to the last hour, and the count of transactions is > 50. Generally at this point, nothing will show in your viz at all, because you've filtered everything out except when you want to be alerted. I always recommend checking the historical data to see how many times you might be alerted, or what situations you should really be ignoring--so you might create a new sheet and play with the filters to see what the signal to noise ratio is going to be.
3. Once you're satisfied, publish the viz up to Tableau Server and subscribe to it on the hourly Alerts schedule that you set up in step (1). At this point your alert is set up to notify only you. Let it "bake" for awhile until you know it is working as you wish.
4. Anyone else who wants to receive the same alert can then subscribe to the same viz, on the same schedule, and be alerted in the same way. That's one way of getting the alerts to the managers.
Bonus: If you know your alert is working, and you want to control who the alert goes to more precisely, or send it to an entire email alias without anyone else having to subscribe to it, convert it to an Advanced alert as the documentation describes. If after you've gotten steps 1 through 4 done, and are happy with the results, I can assist with this if it's not clear from the docs how to do it.