Measure numbers: start #1 later on in the score

Right click the measure and change the field that says "Add to Measure" -4, so the 5th measure is called measure 1. Alternatively you could right click each of the first 4 measures and click "Exclude from measure count" in measure properties.

Note: the status bar at the bottom of the window ALWAYS counts EVERY measure, the above will only affects the measure number displayed on the score.