How to create and use a custom data type that contains a geometry and an int?

Hi! I am trying to create a data type "IndexedGeometry" that wraps up a geometry and an int as an index, and I want to write a "Sequencer" component that automatically assigns indices to geometries and output this IndexedGeometry data. Could anyone tell me:

1.Which interface should I implement or which class should I inherit from to create this new data type? (I tried to inherit from GH_GeometricGoo<IGH_GeometricGoo>, but when I test my component, I get "Cannot create abstract class" runtime error.)

2.I guess I need to write a parameter that inherit from GH_Param<IndexedGeometry>. If so, what code should it contain?

The "Sequencer" component image below might explain what I want achieve better.