Intervals for endurance rides

In order to train properly for very long amateur solitary rides (+250k; +4000m up), I use these workouts on the rollers:

Workout (Interval type), 1/2 times a week:

10' warming up
5' @ 135-150bpm (aerobic zone for me)
5' @ 160-165bpm (aerobic thereashold for me)
5 x (2' easy spinning + 3' aerobic threashold)
5' @ 135-150bpm (aerobic zone for me)
5' warming down

Is it correct? Or should I use different interval times?

Another question: for workouts in zone3 (aerobic zone, 135-150bpm for me) is any variation in HR/cadence needed? And is it better to train in zone3 at high cadence (>110rpm) or at a cadence which is most common on the road (ex. 90-95rpm)?

I'd really appreciate ur opinion...