How to communicate over long distances (60 m) using serial communication from multiple serial devices connected to my PC
In the previous post, recommendations were made to use a RS485 cable. Is it therefore okay to first convert the RS232 at the reader to RS485, then run the RS485 cable to the PC and finally use an RS485 to USB adapter to connect to my PC's USB ports?

That'd work, yes.
But in all honesty, your device has ethernet... Use ethernet. It's exactly what you need to connect many devices over a long distance. No adapters, no hassle. Might even tunnel this through your existing network infrastructure, if any, using VLAN, or encapsulation.
If this is &quot;because my software already supports serial&quot;: debugging software on a PC tends to be easier than debugging long-range serial connection issues. Ethernet is very robust.
Ethernet cables are very cheap. There's industrial connectors for them. They are long range. It's trivial to extend the reach of ethernet, if for some reason you suddenly need more than the typically 100 m to 200 m a single ethernet span can't do.
Use Ethernet. Don't convert multiple serial ports.