Modules are high level structures in the AI. Their defining property is that they are AI-wide, and don’t represent a specific unit.
There is only a single instance of a module. If you need to create more than one of a module, then you should create a new type of entity based on AIBase, and create a module to manage them as a collection. UnitHandler is an example of this.
The decision of which modules are loaded and instantiated is made in modules.lua