Questions about a relay controlled AC fan setup
The max input current for this SSR is 12 mA, so you have to use a current amplifier. It can be for example any general purpose NPN BJT connected with a common collector. I suggest using 10 V power supply for this BJT and using 0 V / 7 V DCA output for switching. Do not go to +10 V! This may damage your DAC.


Alternatively, you can use a general purpose N channel MOSFET with "logic level" switching. Then you have to drive it by 0 V / 10 V from ADC.


No, SSR switch operates "smoother" for its load then mechanical switch. The latest one causes several on/off transients (ringing) while SSR switches on only once. So SSR can not damage a fan.
No, you can not force stop the fan by this circuit. You need a special motor and a special switching circuit with "break" resistor (or more complicated means to return energy) to stop rotation quickly.