I think it might make more sense to just return Australia to a single territory rather than two.
I have tried games before testing the idea of splitting islands across sea zones (basically a reverse definition) it has the effect of making bombardments more significant, and fleets less likely to engage on attack (they tend to camp defend relying instead on amphibious.) Splitting islands also increases fighter movement in a somewhat overpowered way, so you have to be careful. I think with an interesting starting unit placement you can accomplish a lot. Australia as a single territory would have greater reach for any fighters landed there, and the scale of the territory warrants it a bit more then solomons.
I think the best approach is to tilt Japan slightly counter clockwise at the southern tip of the island to make more room for ships. And then put the alignment for the smaller islands based of the relative distance between Australia Hawaii and the three major island territories (East Indies, Borneo, and Philippines). I will play up the focus on the key islands (though some of those chains were involved Palau and the Marianas and such. On the whole though I think the stepping stones out of W. USA would be the most interesting way to change the Pacific dynamic. Force both players to defend their coastlines instead of drop south so easily with everything.
Will redraft it sometime on Tuesday when I get a break from work.