From what I've read, around the 500VA mark is where a soft start begins to be useful, and anything below 300VA really doesn't benefit at all. I think at 500VA it would be unlikely to trip a fuse unless you power up under full load, which would (hopefully) never happen with a CNC machine. The soft start is just a bit kinder to the drivers, hopefully extending their lives a bit, and also kinder to the supply and other appliances connected to it.

I intend to run a power line filter upstream of this module, I've heard the TDK Lambda RSEN-2030L is good? As far as I can tell the -L version does not use Y-caps which I think is the right approach in our case

Of course yes, things like E-stops are more important, I'm just fiddling round the edges at the moment.

Anyone using differential signalling on their E-stops by the way? That's a module I've been thinking about building at some point...

https://product.tdk.com/system/files...log/rsen_e.pdf