Geez. This is a huge question! You do a hard-easy schedule to allow your body to recover & to keep the mileage going. Meanwhile, while all this is happening, you have strengthening of your heart, muscles, & tendons, & increasing your mitochondria & aerobic capacity...and so much more. Doing 90+ minute easy runs is more like another workout.
But, your name implies you´re Working Towards 100 & I´m assuming 100 MPW. I would highly recommend getting some books to help you understand WHY you´re doing what you´re doing. You also never mention how long you´ve been running. Going 0 to 100 is crazy! Think about WHY you´re doing the workouts you´re doing too. Why that workout & why at this time?
I would recommend some Arthur Lydiard, but, maybe, Ron Livingston´s ¨Healthy, Intelligent Training¨ (because some argue he sums-up Lydiard in most clear way). Forgive me if you already know a lot of this, but Lydiard is Godfather of Mileage. This appears to be what & where you´re heading.
But, grab Jack Daniels & Brad Hudson &, maybe, some Greg McMillian & Hanson Brothers. Thereś lots of great books out there. Lore of Running, but that thing is a freakin´ bug squasher (and not as much of a page turner as the previously mentioned books)!
I´m sure there´s lots more out there, but this will get you started.