Mod support for grand strategy games?

Hi everyone!

I’m new to UE4, coming with a little experience in Unity and more general programming with high-level languages.

I’m planning to make a grand strategy game. The idea of grand strategy is, basically, something along the lines of the Total War games, without the battles, i.e. just an strategic map divided in territories, provinces r areas, which you can click and interact with. (I plan of course to also have “armies” as single models standing in and moving between provinces, but that is not my concern right now).

What I want is the game to generate the in-game 3d world map for a bunch of simple image files: mainly the next ones:
-one with patches of unique color. The area covered by each unique color will be made into a “province” object. The game thus should render the map divided in provinces, also rendering the borders between two provinces as distinc objects (for example, I want a border to have a material if it separates provinces of the same country but another if it separates provinces of two independent countries).
-one with a number of unique colors, to determine which texture is applied to the map in-game.
-one with color codes standing for altitude levels, to generate the terrain elevation in the 3d in-game map.

Also, the game I want the game to have a system of “stories”. Basically, a story is a chain of pop ups that the different players get over time adding flavour to the game and also changing the game state.(e.g. an story could involve a rebellion in one area destroying some infrastructure).
As I want the game to be as accessible to modders, I want to create a custom scripting language that be simpler than C++ for the modders both be able to customise the layout of UI elements and script their own “stories”.

So, my question is, what things should I learn to be able to perform these tasks? Can you point me to any learning material more or less specific to these topics?

Thank you very much in advance!