I have much the same problem! I am in the process of using Raspberry Pis to control my model trains. I have sensors in in the tracks that are connected to GPIO pins. I need a network of Raspberry Pis to control my whole system but only one of them needs to be a model 3, the others can be these new Pi zero Ws.
I've spent the past 2-3 months slowly learning about hardware with cheap ESP8266 boards. So much fun wiring small wifi-enabled boards to random sensors and output devices.
I suspect I'll graduate to using PIs in the future, I used to own one that was solely used for emulation, but it didn't survive my international relocation.