Hi Dan
I have a similar setup to what you have. In my case it is a Raspberry Pi 3 on the mount (vs your Pi Zero W), an Aaeon Up computer (vs your RPi4) on the scope and a Windows desktop (vs your Windows laptop).
On the RPi3 I have Ubuntu 20.04 server installed, INDI and INDI Web Manager . The wifi is set up as a hotspot. The clock is set up to synchronize from the Aaeon-UP. It connects only to the mount via USB
On the Aaeon UP I have Ubuntu 20.04 desktop installed, INDI, INDI Web Manage, PHD2 and chrony. The inbuilt wifi connects to my home wifi network . A wifi dongle connects to the hotspot. PHD2 uses a direct connection to the guide camera rather than INDI (not necessary but it works better for me). In INDI Web Manager I define a remote connection to the RPi3 INDI driver. chrony acts as a NTP server for the RPi2 to sync to as it cannot access the internet. (except when I connect the LAN). Connected to this device are the guide and imaging cameras, filterwheel and focuser.
On Windows I have KStars/EKOS installed which connects to the INDI server on the Aaeon-UP (and which in turn chains to the INDI server on the RPI3). I also installed TightVNC to talk to the Aaeon-UP.
INDI Web Manager starts automatically on the two Ubuntu machines and starts up the required drivers. I then start PHD2 (via VNC connection from Windows) . Then I start Kstars/EKOS (actually the order is not that important). Select a target in Kstars, unoark the mount slew. Then in EKOS platesolve to align on the target and from these use EKOS to focus and start capturing.
I currently haven't automated the startup of PHD2 not star selection and guiding initiation from EKOS but I believe that is possible.
I'm happy to provide more info on how to set things up - as much as I can remember
- or you can use the various guides/tutorials