So... Here is the list of the components (concepts, pictures, 3D models, pieces of codes) I'll try to borrow from modders in order to have a mod far more easy to make. Of course, before anything, I must obtain their agreement, and this is why I'll begin to send demands today (8th May) before initiating the "training phase".
If a creator has accepted that I use its creations, I'll indicate this with a

next to the elements.
Of course, all help is welcome.
Gazebo won't be named very often, but that is simply because I'll ask myriads of things (mainly codes and pieces of advice I think).
Austria :
- Janboruta for the Landwehr icon and flag

- bernie14 for the Landwehr 3D model

-
JFD 
and/or Gazebo (Exploitation policy) for pieces of codes for the promotion of the UU
Babylon :
- JFD

- Janboruta for the Kibitium icon and flag (this
mod)

- Danrell for the Kibitium 3D model (idem)
Byzantium :
- Kwadjh for the Hippodrome icon (this
mod)
Carthage :
- JFD (for this
mod)

- Janboruta for the Shophet icon and flag (idem)

- Danrell for the Shophet 3D model (idem) and the Numidian Cavalry (this
mod by mikeburnfire)
- mikeburnfire for obtaining the name of the one who has created the icon and the flag I want to use for the Numidian Cavalry (idem)
Denmark :
- JFD

- Janboruta for the Longship icon and flag (this
mod)

- Wolfdog for the Longship 3D model

- Barathor for the Ting icon (from the
Viking longhouse by mikeburnfire) => I'm not sure about using this icon (since most picture shows the things as outdoor assemblies), but it would make a good placeholder.
Egypt :
- JFD

- Janboruta for the
Kopesh icon and flag and the
Nilometer icon

- Danrell for the Kopesh 3D model
Ethiopia :
- sukritact for the Monolithic church icon
France :
- Hypereon for the
Grande Ecole icon
Germany :
- JFD for the codes of the
Jaeger 
- Janboruta for the icon and the flag of the Jaeger

- bernie14

and/or Danrell for the 3D model of the Jaeger
Greece :
- AlanH for the
Agora icon
Indonesia :
- mikeburnfire for obtaining the name of the one who has created the icon I want to use for the
Wayang.
Japan :
- JFD for the
Daimyo 
- Janboruta for the icon and the flag of the Daimyo

- Danrell for the 3D model of the Daimyo
Mongolia :
- lincoln-lyf for obtaining the name of the one who has created the icon I want to use for the Yassa court (from a Mongolian
UB of the Super Power - Clash of Civilizations mod).
Poland :
- JFD

- Janboruta for the icon and the flag of the
Voivode 
- Danrell for the 3D model of the Voivode
- mikeburnfire for obtaining the name of the one who has created the icon I want to use for the Barbakan (from Barbacan, Polish UB in this
mod by mikeburnfire)
Polynesia :
- More Civilizations
- Janboruta for the icon and flag of the
Koa 
- Hangman for the 3D model of the Koa
- TPangolin for the icon of the
Fale Tele
- Pouakai - for permitting use of the Koa component from the
Polynesia split.
Russia :
- Janboruta for the icon and flag of the
Streltsy 
- Sukritact for the icon and flag of the Pogost (taken from the
Sobor UB, since it looks alike the Vytreba pogost)
- Wolfdog for the 3D model of the Streltsy
Spain :
- BlackFeather_ for the icon and flag of the
Armada
- lincoln-lyf for obtaining the name of the one who has created the 3D model I want to use for the Armada.
Sweden :
- JFD for the Stavkirka (from
Stave church)

- Janboruta for the icon of the Stavkirka
The Aztecs :
-
mikeburnfire for obtaining the name of the one who has created the icon and the flag I want to use for the Eagle.
- Danrell for the 3D model of the Eagle.
The Celts :
-
mikeburnfire for obtaining the name of the one who has created the icon, the flag and the 3D model I want to use for the Carpentom.

- TarcisioCM
- Leugi for the icon and the model of the
Oppidum
The Incas :
- Leugi for the icon and flag of the
Chasqui
- mikeburnfire for obtaining the name of the one who has created the 3D model I want to use for the Chasqui.
The Iroquois :
- mikeburnfire for obtaining the name of the one who has created the icon and the flag I want to use for the Prowler (from the
Rusher).

- Patum333 for the 3D model of the Prowler (idem).
The Mayas :
- Leugi for the 3D model of the Holkan warrior (from the
Konuks'wu)
- Janboruta for the icon and flag of the Holkan warrior (idem)
The Netherlands :
- JFD

- Janboruta for the icon and flag of the
Goedendag 
- JDF for obtaining the name of the one who has created the 3D model I want to use for the Goedendag
- wodhann for the icon of the
Waag
The Shoshones :
- mikeburnfire
- Neirai for the concept/codes of the Hunting pound (from the
Buffalo pound)
The Zulus :
- mikeburnfire for obtaining the name of the one who has created the icon, flag and 3D model I want to use for the Induna (from the
Izinduna)
So the people I'll contact will be
Gazebo, JFD

, Janboruta

, bernie14, Danrell, Kwadjh, mikeburnfire

, Wolfdog

, Barathor, sukritact

, Hypereon

, AlanH, lincoln-lyf, More Civilizations, Hangman, TPangolin, Pouakai, BlackFeather_, TarcisionCM, Leugi, Patum333, Neirai.