Making a mod is tough. It's a lot of work and things go wrong that you never expected to have a problem with. It has to be something you really want to be doing or it quickly goes from "fun" to "work".
The way I usually start is I sit down and I make the first quarter of the map. Just where the player is going to start and the surrounding area. I'll populate it with some NPCs or monsters, and just piece things together.
After that I make my first part of my main quest. That way I can build the map around what I need the quest to be. From then on I continue with a mix if mapping and questing and scripting. I kind of do it all at once.
Scripting is a big part of Divinity modding. Every action you want to have happen in your game requires you to script it. It' a very basic scripting language - definitely easier than (though sort of based on) C++.
The thing you'll need be able to think about are IF -> THEN logic, an INTEGER vs a STRING vs a CHARACTER vs a TRIGGER. Those are the big parts that once you get a grasp on, the rest comes pretty fast.
Of course you'll be able to make a mod, but the question is, will you be willing to learn how?
