How to Model a Transformer in LTSpice
So what is the best strategy to model this step-down transformer?


You have to find something in the data sheet that tells you about the no-load primary current (aka magnetization current). Then you calculate what the primary inductance will be for the voltage stated. It is going to be henries and not micro henries so your 2nd graph appears more reasonable.

Secondary inductance is smaller than primary inductance by turns ratio squared.