Critical evaluations and optimizations of the (Na + X) binary systems (X: Ag, Ca, In, Sn, Zn) are presented. The enthalpies of formation of Ag2Na(cF24_Fd3¯m), InNa(cF16_Fd3¯m), NaZn13(cF112_Fd3¯m) and InNa2(oC48_C2221) were estimated from First-Principles calculations. The Modified Quasichemical Model in the Pair Approximation (MQMPA) was used for the liquid solution which exhibits a high degree of short-range order. The solid phases are modeled with the Compound Energy Formalism (CEF). All available and reliable experimental data are reproduced within experimental error limits. The integration of finite temperature First-Principles calculations provides a useful and effective assistance to the Calphad modelling approach. Finally, the short-range ordering behaviour of (Na + In) and (Na + Sn) in the liquid solution is studied.