Ga - Culture
When it comes to Ga- culture I would make it so that there is one main city (Ga-Metru) thats also the religious capital , being the seat of the Justicar like order, as well as the Temple of each of the Elemental Deities. Ga-Metru would have buildings that are soild, biggest example would be the inspiration taken from Zoras Domain from Zelda.
Have it so that the Main City is above water like this, having a main entrance to the sea as well as being enclaved between the cliffsides.
I imagine Ga-Metru being like this during night time, sorta like if you took Glowing Algae and encorporate the glow aspect into the buildings.
Instead of a King because they are Matriarchal, their main leader is a Queen, which has an advisor from the Justicar order.
The rest of the settlements are prefabricated or interconnected fishing boats made also into houses.
also sorta like Pony Island from Pokemon they have a walkway that connects the land to the sea and the boat houses to each one.
Main weapon of the Ga-Soilders /guard is a Trident.
Funny points: With the examples TTV crew made, Ga- culture would be close to Zora, but Le-Culture would be close to the Rito, Ta-Culture to the Gorons, and Po-Culture to the Gerudo. Maybe the Onu and Ko cultures can be different mixtures of the Hylean one.
Le - Culture
Le- people would bring you mail like the Rito. Thats also their main export, its postal service and air transportation.
Their Guard would use Bows and Arrows as their primary weapon
Le Cities would be like the Rito village.
Being situated in the mountains, buildings constructed like bird cages
Po - Culture
As stated they would be sorta like the Gerudo, the market people,
I would also add in like how the Gerudo also mine gems (precious stones), the Po people can also do that. Have them also be the ones that use gold a lot due to the sheer wealth they have (also gems and other stones) in their design.
At least have their leader be the one with gold on him / her.
Would also add in that the Po people would be skilled architects, sculptures, being able to craft beautifully designed stone buildings, metal accessories, and general sculptures.
Their cities would be around massive lava flows, and generally very got for everyone.
Like the Gorons, they would be master craftsmen when it comes to weapons, shields , and armor. Also sumo wrestling would be a cultural thing for them.