You are right, Flap 4 is the same as Flap 5. The reason is that this slat/flap position can be used for take-off and landing. But each has different protection rules. For take-off, you want the config warning system to detect that the correct flap position has been chosen and for a landing, you want the EGPWS and Flight Warning computer to determine that a valid landing flap position has been selected.
As for flaps usage, I'll normally pop onto the glide with Flaps 1 with Green Dot plus 10 or so. At five miles select gear down and Flaps 3. At Flaps 3, re-select Green Dot and at three miles, Flaps 5 or Full and Vfas. It keeps the noise down, you are easily stabilised by 500' and works nicely. But when ATC demands something different or on horrible days a different schedule may have to be followed.