They are an excellent interval distance for both hard 5k pace intervals and for tempo intervals.
5 x 1k at slightly faster than 5k pace will really beat ya up, so once a week is enough. I would alternate that type of workout with a race.
A good tempo workout with Ks is something like 6-8 x 1k at 8k-10k pace with just 1 minute rest jog.
Alternate that with your 20 minute tempo on Wednesday’s to keep things interesting. Also I agree that your tempo pace for the 20 straight minutes is too fast.
You can tack some very short hill sprints (10-15 seconds) or strides (20-30 seconds) on after the tempo to work on race “speed.” Nothing crazy but just get the wheels turning after your legs are somewhat fatigued. Be sure to get at least a minute rest between.
Another Tempo workout I like is 2 x 5k around at half to marathon pace with 5 minute rest. Do this one occasionally too.
Here’s how I would set up your week...
Mon: Easy with Very Short Hill Sprints or Strides
Tue: Easy with Core work
We’d: Tempo Type Workout with Very Short Hill Sprints or Strides
Thu: Easy with Core work
Fri: Easy with Very Short Hill Sprints or Strides
Sat: Race or a Hard Interval Workout
Sun: Easy Long Run