What style are you shooting for - have the Eternals changed since their days on Earth?
From the examples of the book, Zeus seems to have become more sophisticated (secret police and extensive filing system), as has Hermes, Aphrodite (romance as well as lust), and on and on. In short - how much do _you_ imagine them varying from classic reference resources.
Also, would they use 21st century toys?
The sample art shows Ares (or one of his followers) lugging around a squad automatic weapon. So would computers (or their equivalents(babbage engines, etc.)be found out in the 9 Worlds? On this note I doubt the most convenient things (like cell phones and their ilk) would exist outside of the most sophisticated and urbane locations (Helios and Mercury Station).
On a related note, - how purely Greek a setting are you imagining?
For me at least, the example of Metamorphosis the use of centurion and lieutenant were a bit jarring. I get the impression that the creator and the Eternals chose the bits they like from history and used them. Am I even close? Reason I ask is I have this image of a sophisticated military set up - high tech weapons, etc. They are briefed on the plan and then pull out bulls for sacrifice to Ares (for victory) and Hesphateus (for the gift of the gear and so it doesn't break). Or an operating room where Apollo is invoked before they begin surgery.