No reason to do long runs at this early level. Maybe 4-5 miles tops for this goal.
If somebody can't get you < 5 on 30mi/week, they probably shouldn't be coaching.
Varied paced training, w/ moderate volume is far more effective.
You want to develop speed and stamina together. As you get fitter, your training pace should fall faster than your volume goes up.
You need 62 400 speed to go < 5
You need 52 400 speed to go < 4:10