When using Google Mail, are all separate contact lists referenced when creating an email or do I need to merge/combine all my lists into one? If I do need to combine the lists, how should that be done? Thank you!
Yes, they are all referenced, you don’t need to combine them. You can easily test this by adding a different test contact with the same name but different surname to each of your lists (e.g. John List1, John List2, John List3, et cetera) and then try composing an email to be sent to John... You will see that all of them appear in the autocomplete list.
As for combining the lists, I’m not sure you can do that at the lists level, but you can easily move the contacts from one list to the other, or make them (all or just some) belong to more than one. The lists behave just like the mail folders, they are virtual—they are just labels/tags. When you select some or all the contacts in a list, a new button appears at, in the menu (see image below), that gives you the possibility to move/remove the respective contacts to/from your lists.