I think the idea is quite solid and a second game of this type would get more players.
Regarding the water provinces, the map was handed out for perusal before the game started and which nation starts where was unknown, so any disadvantage the nation with out direct access to the water province is no more or else than the disadvantage another nation has for having less gem income or less gem income of the type that is useful to him. Regarding fighting for the water provinces, I'm sure there'll be more of that, we're barely two weeks into the game after all. Plus with easy access to flying items and teleport spells, I don't see why any nation would have no access to the water provinces and experience the subsequent retaliation
Regarding the number of players, it doesn't matter how many players a game has, some will be at peace, some will be annihilating each other, some will be winning, some will be losing, and some will be fighting multiple opponents at the same time!