Hardware Recommendation

I get it! Its a big machine so you do need wireless. But you should not consider  USB.
I would look at this pendant which has a 433 Mhz receiver and designed for industrial use. Pair it with an external antenna at the receiver end.
www.wixhc.cn/product/433mhz-manual-pulse-generator
Unfortunately, you still end up with those 20 odd wires but they are contained in the control box.
These work really well with a Mesa card that has  a MPG input built in (eg 7i76e etc). For Ethercat, you would need an encoder input which are pretty costly. Note the Estop is  dual circuit so designed to work with a safety relay.
There is a fair bit of custom hal code to get these going.

Note Ethercat adds an additional layer of complexity to a linuxcnc build and it was hard work when I built my machine. But it is a lot eaiser today with efforts from myself, Scott Laird and others...

At a minimum I will tie a wire to my pendent, and hot glue and E-Stop button.
About the choice of going EtherCat, if I stick to a system that advertises cia402 adherence, should LinuxCNC be able to control the drives, without me writing code, has the hard work been done?

Cia402 is definitely the way to go.You can follow my basic cia402 example for the Rtelligent ECT60/86 drives. github.com/rodw-au/linuxcnc-cia402
Note that there are two xml files that include a config for a Rtelligent I/O module and another cheaper and more basic deiwu I/O module.
I like the Rtelligent as they are well documented for a Chinese drive and now include servos in their range (Which I have not played with). Another drive we played with only had a couople of registers but we got it moving.
The Deiwu I/O one was built based on output from the ethercat pdos command.

Note that for ethercat, you have to build your config in a text editor as there is no config tool. Having a basic config like I have shared gives you the framework. There was a time when there was no support in pncconf for a lot of cards (like the 7i76e  I started with)

 

Well I received an apparently detailed manual from www.lichuanservomotor.com. It's 83 pages, and in English.
Unfortunately it is 9MB+ so I can't upload it. About 350CDN delilvered.

EtherCAT Lichuan Servo Kit 750W 2.39Nm Servomotor EtherCAT For CNC Multiple Axis, Easy wiring, With 3 meter Cables

www.aliexpress.com/item/1005006702561572...arch%7Cquery_from%3A