RS-485 circuitry and software control

My RPi-as-HMI communicates with the MODBUS Slave upon the RS-485 line. It's a well-known fact that there is a strong necessity to use isolated solutions in the industry, medical devices and for a noisy environment (Intersil note on the issue is just an example). So I have to follow the trend.
I want to note the hardware and software sides of the Raspberry-RS-485 topic.
Below I note, step-by-step, my research. Most of it happened to be in vain. The result is simple. But I want to keep all branches, just for myself.

Hardware 

Here is an extended illustration of the RPi-as-HMI structure: