Emergency Stop Circuit

I think the idea of daisy chaining e-stop to e-stop isn't a great idea, even with LEDs. I think the LEDs fitted would also void the safety rating provided as it wouldn't be standard usage circuit recommended by the OEM.

What I've seen in the past being a bigger issue than "where the E-stop was activated", is when an E-stop simply fails and stops production, you have to pull the cover off each e-stop and set of wiring to test and find the fault. All wires back to the panel you can easily test one by one at the terminal blocks to source the issue.
If an LED is required for indicating the position there was an actual e-stop actuation then you should run an additional 2 cores in each cable to a normally open contact inside the E-stop though your e-stop might not have this ability?

As stated, the input resistance should be far below 900ohms so you should be fine all on one safety relay running all e-stops back to the main panel separately. Of course you can go up a size from 18AWG though it shouldn't be necessary (for electrical or mechanical reasons).

That's correct. I'm going to see if they will run an extra 2 conductors to each e-stop that they can later use to power a light thru the unused NO aux contact inside the e-stop. They said the customer doesn't want that but I can see that being a future add-on so may as well plan for it now. My e-stops have 3 NC and 1 NO. I'll also try to get them to run each e-stop (or pair of e-stops) to the panel so it's one spot to troubleshoot a failed e-stop instead of running all around this system to find it. That does cost the electricians more money on wire and they won't be the ones having to troubleshoot any issues. Fingers crossed I can sell them on it though.