with the 20.6 l (5.4 gallons) of water injected in the tank in the fill up step, they can dissolve 16.2 lbs of salt, right?
How this new input (brine volume) modifies the settings, and which are the right ones please?
Your current settings are resulting in 16 lbs salt (=8 lbs per ft3 for your 2 ft3 system) to be dissolved into brine. This amount of brine is appropriate to regenerate 48K grains of useable softening capacity, which is why the appropriate Capacity setting will be 48K (or the metric equivalent).
The controller will automatically convert the grains capacity into gallons based on the Hardness setting that is programmed. With 48K grains useable Capacity, and 38 gpg compensated hardness, this will equal (48,000 / 38 =) 1,263 gallons capacity regenerated each cycle. The gallons displayed (or metric equivalent, likely cubic Metres), may be less due to the amount of Reserve Capacity that was programmed, since Reserve Capacity is usually subtracted immediately.
I did not see a Reserve Capacity amount in the photos. The RC setting will usually equal 1-day of useable gallons, so if your family's actual water use average is 180 gallons per day (3 ppl X 60 gallons each), then the appropriate Reserve Capacity setting will be 180 gallons.
As previously discussed, because 20-minutes is required to transfer the correct quantity of brine from the brine tank to the media tank, the Brine setting should be rightly increased from 60 to 80 minutes.
I suggest a flow inducer... which is something cheap and easy-- a piece of pipe that directs the water flow past the motor.
To clarify, a flow inducer shroud does not replace a CSV, but is a simple DIY cooling device for the pump.
A flow inducer is just a section of pipe to surround the pump, which is sealed to the pump at the top only, above the water inlet screen This ensures all water entering the pump inlet, will be forced to enter the shroud below the pump, thereby flowing tightly past the pump's electric motor, which will remove heat, ensuring the motor will be always sufficiently cooled while it is operating.
In some wells, water enters the casing above the pump, so without an inducer, the downward flow into the pump inlet, will not flow over the motor, so the motor is more likely to over heat, particularly due to the additional heat that accumulates while a pump is forced to short cycle.
pump's output will be restricted by that CSV all the time, will this wear out the pump more quickly?
Pumps are designed to run continuously, 24/7. It is cycling ON & OFF that reduces the lifespan of not only the pump, but also the check valve, pressure tank and pressure switch, particularly when occuring repeatedly within short time periods.
Restricting the outlet from the pump, does increase the outlet pressure, but this also will occur without a CSV, when a pump is installed in a well where the static water level is lower. With an increased static distance, the force (psi) needed to lift (pump) water the increased vertical distance, will be greater.
Because almost all well pumps utilize a centrifugal impeller design, restricting the outlet will not harm them. As restricting the outlet will reduce the flow rate delivered, the pump will not be required to work as hard, so the amount of power drawn will usually be reduced, which will reduce the amount of heat developed in the motor.
As mentioned earlier, a CSV does not restrict flow less than 1 gpm, which ensures there will always be at least 1 GPM flowing into the pump's inlet screen. Although a CSV will reduce the potential for overheating, utilizing a flow inducer will ensure the 1 GPM entering the pump's inlet, will continue to remove heat as it passes over the pump's motor.