Also worth noting, while pipe throughput is unlimited, there is a limit to how many pipes you can physically connect to the network without segmenting them off with something like a pump. For a large foundry array, it's possible you could hit that pipeline extent limit.

Unfortunately, no, in the base game, there is no generic "is full" signal.

You can make it less "manual/tedious" by using parameters in a blueprint. Without trying to type out a full tutorial, it is possible in a blueprint to select a parameter (say iron plates), use a formula to get the stack ...

Likely an issue with having to error handle for all the possible edge cases that could arise when you can already just use a built-in mechanic for bulk upgrades, the upgrade planner. Simple enough to make a blueprint book with the common entities that need upgrades and have some upgrade planners in ...

You can already make an upgrade blueprint for quality and bulk upgrade with it.

Negative counts are useful to prevent an item from being requested.

A simple example that i use for recyclers, in an arithmetic combinator, if i want to make sure my network never has more than say 500 blue circuits, i would do blue circuits - 500.

If blue circuits is 600, the equation would ...

I don't see the grid size itself as a major issue, but rotating batteries is a good idea. I was surprised this didn't work myself when i tried it.

TL;DR
Add the each, everything, and anything signals to the Programable Speaker icon filter UI similar to how display panels are setup allowing for dynamic switching of the icon (and text) based on circuit signals.

What?
Add the each, everything, and anything signals to the Programable Speaker ...