Good changes all around, especially Iceland.
I ended up correcting the AI's instant vassal of Norway issue by making Iceland have its own Icelandic culture. The foreigner malus was enough to deter the fealty 10 days in.
My only complaint is how you drew Suðisland. It seems kind of... odd to me. When I was practicing modding the map (and failing, water provinces are tough...), this is how I ended up dividing Iceland:
I went a step further and created Norðisland, then split it into Norðisland Vestra and Eystra. (I went off
this for borders) But my suggestion would be to put Suðisland (bright red) where I have it (more in Vestisland instead of Austisland), then leave Vestisland with the rest and Austisland as is. Just my two cents.
I don't claim to be an Iceland expert, I just like playing on little remote islands.