In general, you can’t reuse anything because your devices are different physical objects. Your Thing defines this physical object, and the Channels define the properties of this physical object (relay, temperature etc).
Items are openHAB’s internal variables which attach to the Channels. You can attach more than one Channel to an Item if you want, but really the idea is that you have one Item per Channel.
So whilst your physical objects may have the same model number, they will be located in different places, and have different functions, and most importantly have different identifications. So they need individual Things, Channels and Items. That’s not too say you can’t copy/paste the configurations for these - but you’ll have to modify at least the names of the Thing and Item, as these need to be unique. Channels can have the same name between Things as they are referenced via the Thing name.
openHAB text based configs do not support the object and instance pattern. You have to define each instance individually.
You are probably referring to Event Channels. These are Channels that can trigger a Rule directly and are not (and indeed cannot be) linked to an Item.