We rather like visual aids, so we decided to make up a simplified sketch of Amaryth. Just the walls so far. We tried mostly sticking to your numbers and specifications, but the topography did not fully agree.
some specs:Outer city wall:10m tall.
12m thick (ish).
No gates yet (adding those later)
One tower.
Inner city wall:Mostly 15.240m tall (some places needed taller to make sense. Yes, that is equal to your fifty feet)
10m thick.
No gates yet (adding those later)
Eight Towers.
Fortress wall:Varying height. over 100m some places, a bit over 57m in the lowest place.
10m Old Kingdom Foundations.
Thickness is 30m.
Again, no gates yet.
7 Towers.
Topography:Height of tallest terrain point inside fortress is 710m above lake level. But that is 2545m from the shore.
Yes, that can seem pretty tall, but we kept the slope pretty low. For a height increase of about 60m in the outer city, you'll have to go 250m inward.
Anyways, here it is:
Full Size image