EU4 modding and green Africa

Recently I discovered that a couple thousands years BC, Africa was green. Instead of the Sahara there was a huge savannah and the lake of Chad was orders of magnitude larger. I discovered this because I disliked how in EU4 around half of Africa can not be traversed in any way, with most of this area being the Sahara desert.
However, when I found out just how livable Africa used to be, I wanted to make a more grand mod than just adding the wastelands as usable provinces. I wanted to make a mod that would take place in the range between 7000 BC up until 1900 AD, because after 1900 there are aircraft and EU4 can not simulate them.
Thus, I needed to mod the map. It turns out that modding the map requires changing lots of different layers. There are 4 files for the actual looks, one for map textures(which affect gameplay), 1 for how the land is split into provinces, 1 for which lands are water or not and how high mountains are, etc.
The most problematic of those all are the 4 for actual looks, because I'm not very good at drawing on a computer. At that point I gave up.
But yesterday I figured "I may have this weakness, but that doesn't mean I should just accept it."
So what I did was that I opened one of the maps up in gimp and copied the most used colors with color select. Then I tried adding an island next to France and called it Xeaune, which is essentially like Xon, but written like in French. Everything is longer in French.
As I tried the results in the game I noticed no major problems. I had used the wrong map texture, but that was easy to fix. Just a few days before I had given up on the idea of modding the map, but at this point I decided I should make an entirely new one. Modding the existing map on the same quality level is still out of reach for me, but in order to learn I just have to practice. Thus, now I want to make a new map with entirely new geography, cultures and balance. One thing that I'm sure of is that I want to add more islands than in the real world. Sea powers like England were actually quite weak historically. The only reason they were so powerful is that trade practically had to be done by sea. If only ground transport wasn't so thoroughly bad, sea powers would have been much weaker.
However, even in EU4 sea powers are in fact weak if they don't colonize. In order to make England actually able to fight on the mainland I needed to make a lot of changes. Some of those were for fixing silly imbalances in the base game, but some are also just overpowered. For instance, I made it so that if your sea power is higher than someone else's, you can easily declare war. This is a major imbalance and the only reason it doesn't break the game is that those who get the most use out of it are simply weak anyway.
But yeah, I'm going to make an entire new world. Maybe.