I'd like to point out a few things though (I can still only look at the minimap): I think it would be a good idea to open the paths that go counterclockwise.
Then the players will have to choose to expand to one of the 2 sides they can choose from, so the possibility exists that the enemy already chose that base.
If so, then a battle can also take place in the expansions, rather than in the middle.
Now it's pretty straight-forward: everyone picks the base that's clockwise of them and then they can happily expand, not too much trouble involved.