TL;DR
I want to limit the size of the provider chests in a fast way.What ?
I'm using the copy&paste recipe for provider chests a lot ( and its inceasing amount depending on the modules and beacons)So why not limiting the output amount on pasting onto a provider chest.
The number of free slots can also a result of what can be produced in a certain time ( also depend on the modues)
So placing an assembling machine, select recipe, place a requester and provider chests and then a single copy and 2 paste clicks and voila.