Nice development then. Before finishing the campaign, may I suggest adding a roguelike feature? divide a map in triangles with each vertex being within a random 3D radius, and each triangle of a specific type (city, harbour, forest, etc). Using Perlin noise, you could have a mode where every mission is different, allowing you to have people playtest an unlimitted ammount of configurations to check for bugs or combinations you'd like in storymode. 5 minute runs are fun, and better than 1h grindfests, shortness in this is your ally as a small dev, embrace it since it keeps things fresh and more akin to the genre.