You can pull a few quotes about Ossiriand before it became Lindon after the sinking of Beleriand. About it being where Luthien dwelled, specifically Tol Galen. How some Elves that dwelled there participated in the wars against Melkor. But nothing describing Lindon during the Third Age. There's nothing that describes Mithlond in writing. Just the many ships and the road leading to it. It's all conjecture, imagination, and common sense when studying where towns would be and population distribution. (Speaking as someone with experience on the matter as a project leader/Elvish expert to a degree *cough*). Consider this an unleashing of creativity and freedom. You can make massive cities or hardly anything at all.