Ford has never been noted for accurate fuel gauges, at least not in any of the FoMoCo products I have driven (and that cover the last 30 years). When the gauge gets down to the 1/4 mark, it is time to get thee to a fuel station.
My past experience with an intank fuel pump after running out of gas was that it died soon after. With that in mind, you might want to go ahead and replace it while it is more convenient...the in-tank pump does not lend itself to a do-it-yourself at the side of the road like the older mechanical pumps, and when the Mustang pump died, it was a very sudden death
