Is a Synchronous Step-Down Converter powered from industrial 24v a good choice to power a 3.3 volt MCU and sensor ic?
A switching step down power supply is always the choice if you want to limit the power loss in the voltage level conversion. This can be especially important for battery power sources or if there are regulatory requirements on standby power consumption. 

It is fairly easy analysis to compute the power loss in a switching regulator versus a linear regulator based upon efficiencies. Then add that to the actual power that your load circuit requires and this will give you an idea of the total Watts power used by your device. Then you can evaluate it that total power consumption fits the usage market for your device and check if the corresponding power dissipation fits within the thermal envelope for the product.