Build a New Module referring To Another


I would like to know how could I create a new Module and make Reference to another, let me explain it better.

Actual Modules used:

Case - Where users create customer’s tickets and treat them.

Customer - where I register customers and associate them to the cases. (screen attached).

Now I would like to create a new Modulo to register customer’s equipment (hostname, ip, windows version, ID, etc)
and associate the equipment with the Customer, so I can create X equipment for one customer.

When I create a case, I would like to select the customer and depends which customer I select I would load the equipment of that customer and
include them to the Case

Case > Customer > Equipment

1 Case > 1 Customer > X equipment (where X could variate from 1 to 10 for example), depends what the Case is related to.

I was thinking about a dynamic drop down list, but in this way it would be very poor of information.

Could someone give me a hint of how to start this process ?

Thank you in advance for your patient