You show that its an acidic salt by showing that NH4 is the conjugate acid of a weak base, thus NH4 will have the potential to donate a proton back to OH- as seen in NH3 + H2O -> NH4 + OH- so if NH4 has the potential to donate a proton, then in the reactoin NH4Cl + H2O -> NH3 + Cl- + H3O+
therefore NH4Cl is acidic. I' not quite sure how to tell the conductivity i mean if the arrow is single then its definitely a good conductor, but like u said its in an equilibrium, if thats the case then its not a good conductor since it won't 100% ionize.