Is it possible to create a parallel SPI network while using only a single slave select?
SPI is a no go for this application. Generally, SPI is used for high speed, on-board communication lines with a total distance of a few meters at most. It is not something you would use to draw out to 144 different network nodes over larger distances, because it would lead to horrible immunity. Particularly so in &quot;noisy&quot; environments where you activate a lot of motors or coils etc.
Professional alternatives to consider in this case is CAN or RS-485. Either comes with rugged differential signals. CAN is overall the more modern and slightly more reliable option, but might restrict the choice of MCU a bit.
On the topic of MCU choice, we don't use Arduinos for (anything, including) industrial control, for the same reason as the surgeons at your local hospital don't use &quot;My little doctor&quot; toy kits for kids when they operate you. Again: EMC, safety, reliability. But also because we'd like to pick the MCU most suitable for the requirement spec, rather than picking a tool first. Also, 8-bitters are horribly slow and hard to program in C, they are a thing of the past.
In this case your favourite flavour of Cortex M with an on-board CAN controller seems like an ideal choice. CAN is particularly nice when broadcasting data to multiple nodes, because it does that by default: every message sent is always sent to every node in the network. It is up to the individual nodes if they should respond to the message identifier or not. You minimize the amount of time multiplexing. Also with CAN being properly standardized, you can buy standard M12 etc 5 pin connectors and cables, no need for re-inventing the wheel.