If you have natural turnover your 400m shouldn't suffer at all. You'll have a better fitness level from training at 800m. Be sure that your coaches or whomever you are involved with give you speed work. I have seen half milers come down to the 400 and run 48-50.
Here is what I suggest
Monday – 3-5 miles at 5k pace +2:00 per mile slower
Tuesday – 5-7 mile at 5k pace +2:00 per mile slower
Wednesday – 3 miles at 5k pace +2:00 per mile slower
Thursday – 5 mile at 5k pace +2:00 per mile slower
Friday – 2 miles at 5k pace +2:00 per mile slower – 6x30m surges -2 mile cool down
Saturday – 6-7 miles at 5k pace +1:45 per mile slower
Sunday – off
Monday – 40 min. run work the up hills
Tuesday – 3 miles at 5k pace +2:00 per mile – 1×1 mile at 5k race pace – one mile cool down
Wednesday – 3-5 miles at 5k pace +2:00 per mile slower
Thursday – 5 miles at 5k pace +3:00 per mile slower
Friday – 2 miles – 6×600 @ 5k race pace – 400m jog recovery – 1 mile cool down
Saturday – 4 miles at relaxed pace – enjoy the run
Sunday – Day off
Monday – 3 miles warm up – 2x200m hills sprint up/shuffle down – 2 mile cool down
Tuesday – 3-5 miles at 5k pace +2:00 per mile slower
Wednesday – 2 mile warm up – 2 miles at 5k race pace +:30 per mile slower – 2 miles cool down.
Thursday – 7 miles at 5k pace +2:30 per mile slower
Friday – 4 miles at 5k pace +1:00
Saturday – 7 miles at 5k pace +2:30 per mile slower
Sunday – Day off
Monday – 2 mile warm up – 5×800 @ 2:25 – 600m jog rest – 2 mile cool down
Tuesday – 7 miles at 5k pace +3:00 per mile slower
Wednesday – 5 miles at 5k pace +2:00 per mile slower
Thursday – 4 miles at 5k pace +:45 per mile slower
Friday – 2 mile warm up – 4x200m hills sprint up/shuffle down – 2 mile cool down
Saturday – 6 miles at 5k pace +3:00 per mile slower
Sunday – Day off
I would type more in, but I'm getting tired, but this might be something that could get you started. As it would progress you would get involved with 200s up to 900s etc that would speed and towards goal pace for your race.