I don't get why nobody has corrected you on this yet... THAN is for a COMPARISON. THEN is a CONJUNCTION referring to a TIME.
Example:
I run faster THAN they do.
I went for a run and THEN I went home.
As for the actual thread, my suggestion is to follow the easy summer mileage pattern some outlined previously. Imagine trying to be in shape to run your 800 PR (2:00) for six months straight. Pretty difficult, because eventually your body will need time to recover. So if you run your workouts hard all the way from now until the big meets, your body will be very tired by then and you won't do as well. You don't try to peak for months on end. For now, you just want to build endurance.
I like the suggestion someone a few posts before me had: when they do 4x1600, you do 6x1600 if 4 reps won't do it for you. You'll probably be pretty tired on the 6th rep, coming from the 400/800. If not, and you continue to improve with workouts of that sort of volume, you might find yourself capable of a pretty good mile come indoor/outdoor.
I think your coach might have annoyed you less if he acknowledged the workout as an endurance workout as opposed to a "speed workout". Speed workouts are 300m each and shorter, not some ladder workout.