After some checking (my first revision was so great someone ended up closer to an enemy capital than to the allied capital), I have ended up with the final version of the .map file.
Its characteristics are as follow: there is one province between the two capitals of the same team, and at least one capital of each team can reach the five other teams in three or four provinces (via the shortest route). There does not seem to be any imbalance, and all starting provinces are connected with several land provinces (at least four, more likely five).
In other words, you may expect some early tension with your neighbours, as everybody should be close to all the other teams. We shall see how it plays out.
