Sounds good guys.
As well as the large sea boards, I've also got a number of smaller grided sea boards (and islands to go with) that could be used at the planning/strategy level.
I've always liked the Peter Pig approach to pre-game play, where you have things like a number of objectives, each of which both sides need to assign at least some of their overall force. Then both sides declare what's been sent to each location, and you play the biggest game (with the other locations being resolved off-table and potentially generating late arrivals/reinforcement for the main game). With our naval stuff, we could do something similar, with potentially more objectives/locations to cover, and play even the smaller encounters.
If we're likely to have a fair few Spanish ships it might be good to set things in the Med or Caribbean, but otherwise the Baltic is full of islands too! Lots of scope for blockade breakers, merchant convoy protection, you name it, as well as straight fights of course.
