It helps to start with a less complex game and learn the basics of how the engine works. I know in Godot at least (and I assume Unity is miles ahead) there are

It helps to start with a less complex game and learn the basics of how the engine works. I know in Godot at least (and I assume Unity is miles ahead) there are prefab things to do what you describe but you will need to know how to fit them together. Another option would be to fork an existing foss RTS game, like Spring, Warzone 2100, BOSwars, etc.