With the map itself mostly done, all that's left is some XML/Lua editing, which is where a lot of the magic (i.e. YnAMP map options) happen.
Beside toggleable rivers that I tried on my last map (Saph's Mediterranean), this time I also figured out how to do toggleable world wrap. It turns out that for a map to be able to wrap properly, its dimensions (both x and y) have to be even (not odd).
Normally, because of realism and practical reasons, TSL maps, unless its of the whole world, should not wrap at all. Still, some players might want island maps like this to wrap, and making world wrap an option to the player is probably a good idea.
Next step: inputting the actual TSL for official and custom civs/city states