[Sombre]

If I could give someone looking to start modding any advice it would be this: Don't start too big.

The absolute best thing you can do is get in a bit of practice with some more minor modifications to basegame first. You don't have to jump right in with a new nation - you could just as easily add stuff to an existing nation, by modifying existing sprites. This would give you a feel for balancing, doing graphics, making units/spells etc and allow you to produce something and get feedback without it taking ages or becoming overwhelming.