Source: - is node name, however wildcards are not supported. But you can make a separate container for your servers - nodes can be present in multiple containers simultaneously. And containers can have auto-bind scripts to add nodes automatically.

Event: - is event name, list of possible options will be shown. It is convenient to configure events with different names for different occasions in addition to SYS_THRESHOLD_REACHED. This way it's easier to dealt with them in EPP rules or search alarms, so your update DCI is a good candidate to have separate event for it.

That's approximately it. In addition you can check DCI summary table functionality - this allows to display table with DCI data accross multiple nodes.
And, also, you can use a container and it's auto-bind script to add only nodes that have some threshold triggered. This way you'll always have a list of nodes that require attention at hand.