Quick update:
This is the roughly symetrical set of islands I found:
Right now, I think that you should only be able to "skip" one island from what you already control, the idea being that if you attempted to go further into contested territory you'd be intercepted anyways. So that keeps you from taking over the home base on the first turn.
For merchant raids, I'm thinking each island has lane of commerce that can be attacked/defended. But you'd also have the option to move cargo amongst your islands instead of shipping immediately, so you can convoy. For combat purposes, transferred ships would be considered at the destination in case the island is attacked, so moving them around carries some risk.
I am considering having a carrier that might influence ground troops strength within a certain radius... such as 1 space for helos and 2 for harriers. If this was done, the carrier would have to be placed in a sea space that could then be attacked. I'm a little concerned with this because it more or less means going after the carrier would be like playing battleship; you have to attack the right space to find it. It might not be worth it; but I definitely want to have DW objects that affect the overall game somehow and this seems like an obvious way to do it.