Will owning sea give me any advantage whatsoever?
Since sea zones are way larger than land zones, they give you a strategical advantage. They have great offensive capabilities if you can get an enemy coastline.
Also, if you have a sea base between two players who are trading, and the ships must enter through your sea zone in order to trade, you can start a blockade, stopping the trade.
And, sea bases will make you able to expand into areas you couldn't reach by land if other nations block your borders (like you've done).
But sea bases don't increase your production, so they're only built for strategical reasons. A war between sea bases is more easy to defend than a war between land zones (again, because they're much larger, requiring fewer ressources spent pr. zone).
You can spend 24 ressources.