The best benefit for the Z4 interval workouts will come from spending as much time as the plan calls for actually in Z4. It does that a minute to come up to full Z4 levels and then some time to drop back to Z1-2 levels during the rest intervals. You should try to get the specified time in Z4 for each repetition rather than just going by the watch time from when you start.
For the 8 sec hill sprints you should take long recovery between. Typically this means walking down hill to the start very slowly for 2-3 minutes.