You have no idea how happy I am to hear it that you can make fortresses that BIG!
I'd keep a Elven twist to it, correct me if I am wrong , but Minas Tirith was built originally by the Elves in lotr.
Uhmmm... Don't you mean the Numenorians? Correct me if I'm wrong. However, I agree, the elven walls would be the best thing for MT.