How to make Map & Battle System like in the Hearts of Iron IV

Hi. I have researched the internet for the 4 days, but have not found any answer to my question.

So the idea is to make something like this:

As you can see there a lot of provinces/regions inside the country…

So the main things i’m interested in:

  1. how to make such world map, where each country will have it’s provinces;
  2. how to make country selection and country border/outline
  3. how to fill each country with it’s own unique color
  4. how to draw such Attack arrows like of this gif.

What I have tried:

  1. make small map with the 3D cubes (about 300 gameObjects) - I got lag spikes when calculating it’s borders, so I thing that’s not the best idea.
  2. tried to make map like here: (but that’s not what i actually wanted…)

Example of the map:

Please, if you have any ideas/experience with that War Strategy game type or made something similar before, let me know how to make it in the best way - without lags and with such flexible battle system like on the GIF below.