1) re: ME work. I normally try to get at lest 8 weeks and as much as 16 weeks of ME progression before shifting to uphill intervals. But you will want to start these Z3-4 intervals no later than you have 5-6 weeks before the event. I typically use 10-15min repeats for this.
2) re: Hill Sprints. Most endurance athletes should have hill sprints in their program all year. This is not endurance training. It is power training. It is meant to increase your stride length not make you faster sprinter (although that does happen as a side effect). Those 3 and 10 min reps are endurance training and good to have but they do not do what hill sprints do. If you’ve been doing hill sprints for a while I suggest doing more than 5 reps. Make a mark at the high point on number 3 and when you can no longer reach that line the workout is over.
I hope this helps.