Lyell: There will be "closed" missions with set objectives in the campaign. There really must be some way for the computer to know you've beaten it and completed the mission, after all

We want to have a lot of variation: obviously various forces opposing each other where the objective is destroying a key unit/airfield, as well as escort, sub hunt, surface only, etc, etc. For most missions, there should be different ways of beating it: getting air supremacy, sneaking in your subs, massive surface engagement, stealth bomb run, etc, etc.
There will also be skirmish missions, which sounds like what you prefer. Since the map is already there, it will be really easy both for us and modders to make several different missions, where you can really try out all the fun stuff we didn't even think about.
Julian: I'm off for vacation tomorrow (so responses here may be a bit slow in the coming weeks), but I'll pass on word to the others to post a picture of the (provisional) map.