SharePoint 2013 wiring together 3 custom lists

In a SharePoint 2013 new project that I will be working on, I am creating a custom list initially for users to pick what items that they need before clicking the submit button where a workflow will be initiated. When I have completed the custom list, I am going to edit the applicable form(s) with InfoPath 2013 designer.

Since this is the first SharePoint 2013 project that I have ever worked on, I have the following questions to ask you:

1. Is my planned way of working with SharePoint 2013 the preferred method? If not, would you tell me what the preferred method is and tell me and/or point me to a url that will show me how to use the preferred method?


2. In the custom list, the user will need to obtain the values for Customer Name and Contact Name from a dropdown list. Basically once the customer name value is obtained from the dropdown list, a list of associated 'contact names' at that company will be displayed in the contact name dropdown list. To obtain the values for the dropdown lists, I am thinking that I should:
   
   
   
   • Obtain the values for company name and contact name from 2 separate lists. Thus can you tell me how to 'wire' the 'company name list' and the 'contact name list' to the 'main' list called 'main'? **I am thinking of using an excel import process to load the 'company name list' and the 'contact name list' with data obtained from the sql server database initially just for testing purposes.
   
   
   • Once I have completed the prior step, would you show me how to connect a sql server database to the 'main' list? **Note: I am not going to use sql server to start with since this is the first SharePoint project that my company will be using?