Did the Ancient Amaurotians... (minor spoilers)

[Lauront]

It's a bit vague, but it confirms at the least that they had distinctive facial features and unique masks. Assuming the city Emet did was to scale, it does seem like they were giant in size - certainly, the NPC remarks in the area (referring to the characters as children) bear that out.

Based on the Ascians' general preference for hosts, I'd venture a guess that they look like giant (midlander?) hyur. As for Emet's preference for his host's form? I take it that he just enjoyed his time as Garlemald's Emperor and thus preferred that body as far as mortal hosts went. We know that he had white hair from his short story.

As to whether they were "human", it depends on your definition; appearance-wise, maybe they were giant hyur, but in terms of what they were, they were very long-lived beings with superlative aetheric reserves and powers besides that, of which the current Echo is but a fraction. So it's a bit of "yes" and "no". They have a similar range of emotions and interests to humans, but their characteristics make them something more.