SIgnal conversion (current -> voltage), robustness of methods
Are the current sensing boards with the ACS712 suitable for this
  purpose ?


The ACS712 measures current up to 5A dc and has an accuracy of 1.5%:


  Total output error 1.5% at TA = 25°C


That means the accuracy in amps is 75 mA. This makes them totally unsuitable for measuring and reporting a 4/20 mA signal.


  For which solution would you opt ?


Clearly the ACS712 is unsuitable.

Try googling for circuits using op-amps like this 0/20 mA receiver: -



You might also want to consider a design that provides loop power: -