My best advice would be to think hard about what type of gameplay would best express the theme of the map, how the "story" of this map can be integrated to the gameplay.
For example, you have cannons on the map. You could give those territories the ability to bombard nearby shores.
As it's a pirate themed map, I'd like to see more ships.
That treasure chest... you could set a high amount of neutrals on it and set it as an objective (hold treasure for one round to win).
These are just examples, but you can maybe use them to get some ideas for the gameplay.
Oh and remember the size limit. Downsizing shouldn't be a problem though, it's a lot easier than upsizing... Personally, I don't agree with the size limit that has been set for maps, as I'd love to see huge and epic maps, but as long as that limit is in place, there's no point in crying about it, it's better to just work with the tools you have available.
Ps. my examples are by no means meant to say that you shouldn't make this a simple standard-gameplay map if you so wish. Merely I wished to express that the gameplay should compliment the theme of the map, somehow.