Well then, let's see.
If the Empire is based on Rome with fantasy influences, then.... I nominate the Tang Dynasty for official influence of the Lhasa area!
Tang is where much of the more fashionable Asian history originates, and was massive influence on the surrounding cultures. From what I understand, many of the quintessential Japanese, Korean, and of course all the later Chinese tropes have their roots in Tang-ear China. Or vice versa?
Anyhoo, China in this era seems fairly cosmopolitan and ... (I hate this word, it's hard to get more subjective in a single word)... progressive. Lots of foreign culture pouring in and being disseminated, altered, cut to fit. Women are fond of fancy hairstyles, dresses are more comfortable and looser, and wearing men's clothing is not the taboo it will be later on.
Also they exist around the same time as Rome so + 1 for getting the empires all time-synchronized.Here's a fashion timeline.
For women's clothes. Men tend to care a little less about their fashion history, so dedicated pages for "Tang Dynastymen's fashion" are hard to come by.
However, a quick Google of "mens tang dynasty clothing" pulls up results like this:
Almost elven, no?
Or... maybe the other way around?
And the armor: two swords, woven scale, topknot. The bracers and greaves are solid instead of splint, and there are definitely boots at the bottom, not sandals, and the swords, though single-edged are straight... but you can see the resemblance?
From the timeline and culture sharing, I suspect the proto-samurai got a few of his dress and weapon ques from these chines soldiers. Obviously there are differences with the evolution over time, and the Japanese went down a path the Chinese did not but still it's close enough to make me wonder.
Also this picture will be relevant.
So, my idea for this land is that; with a Tang base-culture (If indeed the Empire has a Roman base-culture, and the Northmen have a Nordic base-culture), we see each province governed by a wizard of the golden dragon.
Each wizard is more or less free to make laws in his realm, so long as they do not conflict with the wishes of the dragon and so we have a range of regional quirks.
In classic fantasy culture-blend style, to get distinct province flavors I would mix cultures into the base-Tang dependent on geography.
Nanyang is mostly pine woods, and it is somewhat isolated. I would take the black forest tropes, and a dash of Stranger Things and put them in Tang to make a sleepy logging province, who's wizard being far from the dragon, dabbles in the darker magics. The policeman/investigator is a classic character in Chinese opera, so picture the investigator from house of flying knives, except instead of looking for rebels, he's on the trail of secret government-summoned entities.
Each province could be abstracted in this way:
A wizard, a theme, folklore, blended with Tang.
Xianyao could have Rhineland Germany mixed with Tang: people in river valley, defending the borders, plate-armored knights etched with dragon symbols and with silk surcoats.
He already has dragon wings on his helmet: he's halfway there!
Now the hairstyle picture reminded me of 17-century France with the fancy clothes and the powder and the big hair.
And since the Empire has some more modern additions, (sword hilt finger rings, medieval theocratic elements, steel, etc) and is the most powerful empire, so I'm thinking that the current trend in Lhasa is that Imperial stuff is fashionable. You see more and more Roman elements mixing with the culture, perhaps the younger people are in silk togas with scarves and whatnot, or you can find amorphae of gaurm in the local market, maybe Imperial is a second language for many of them, or there are temple of Paragon here and there?
And perhaps the elves get their fashion ques from (to them) distant and exotic Lhasa? Long hair on men, straight single-edged swords, silk - all becoming more popular with the younger elves?
I say this before seeing what the diplomatic status is, so take it with a grain of salt.
Basically I want to avoid the idea that this particular fantasy china is fated to become Han Dynasty, or Communist or what not, and that it isn't just transplanted historical China and really belongs in a world with Imperials, and ancient machines, and Witches, and Elves.