Are there any passive expenses to owning property? (land tax, maintenance, insurance) If so, how costly will they be?

The passive expenses associated with the ownership of property are controlled by the goods and services you purchase to protect, operate, and maintain your land and also the equipment and structures you place upon it. If your land is rich in precious metals and you're concerned about theft, for example, you might procure your own fleet of security drones to keep close watch over your real estate, which will in turn require routine maintenance that you may elect to outsource. Alternatively, you might elect to hire mercenaries or contract with an organization to safeguard your burgeoning empire, either of which will cost you a recurring fee. Automated mining equipment, refineries, power plants, and other modules that you may construct will require ongoing capital investments for new parts and supplies to remain in working order. So passive costs will ultimately be dictated by player choices.