Wow, it's been a while since I've been in a game that will need a map this large. Hopefully the no forging aspect is successful in reducing micro.
Maybe elmokki's Plane of Rusty Nails? Slightly higher prov/player average than I go for these days but not too extreme. And it looks like Cal uploaded a version with 10 land/1 water fixed starts to the server so maybe you could use that as a base to make a NI version (and maybe eliminate the water start as well, though I suppose it won't do any harm leaving it in in case someone else wants to use the NI version with a water nation).
While I don't like the Dominions water nation mechanics and am glad there are none of them in the game (which in any case would be a problem with the lack of magic items) the fact that the map does have some water provinces will give amphibious/aquatic units a chance to shine.
Or maybe Shadowshore? A bit lower provs/player average might help make the endgame more tolerable for the final nations.