The drawing was made with the classic version of ExpressPCB software. I've used it for well over 10 years to design PCBs.
Let me discuss the most rigorous method of wiring. To get some idea of cost I found an eBay site with cable that looks to be a reasonable prices. This is just to get a general idea and not a recommendation. I know someone who bought inexpensive cable only to find out it was copper plated aluminium and not suitable for his use.
https://www.ebay.com/itm/RVSP-2-4-6-8-10-12-14-16-20-Core-Double-Twisted-Shielded-Cable-485-Signal-Wire/254397336055?hash=item3b3b4349f7:g:JE8AAOSwgqZdrqCWMotor wiring would be done with shielded 2 pair cable.
4 core 0.5 mm
2 5 meters US $13.30
Stepper drivers would be connected with 3 pair shielded cable, one pair for each of the three optos.
6 core 0.2 mm
2 5 meters US $11.02
Limit switches would be connected with twisted pairs, individually shielded or grouped into one cable as the physical configuration requires.
More of the 6 core or 2 core 0.2 mm2 5 meters US $5.87
24 volt power would connected with loosely twisted hookup wire to each stepper drive from a distribution terminal block. This is because if they were daisy chained the first part from the supply would be carrying all the motor current and need large conductors. I should change the drawing to reflect this.
There would be many commons and shield grounds going to the same places. On a industrial machine we would use lots of terminals the cost of which adds up fast. For hobby use they could be spliced together. You may have to learn how to solder.
This is a a belt and braces approach to the job. You might get away with extending the existing wiring with whatever scraps of wire you can find but...
Short runs need less protection so you may not need the expense of all that shielding but I don't know the details of your mill. I'd like to hear about the mill and what materials you have on hand. Who are the reputable vendors in your part of the world? Can your friend make recommendations?