Hi, Lori, and welcome to WikiTree. It has a bit of learning curve but the rewards will be well worth it. Nothing wrong with basic questions--in G2G you'll find a lot of people from all over the globe willing to help you with almost anything.
If you imported a Gedcom from Ancestry, you then have to do the GEDCOMpare process before anything in your GEDCOM will appear in WikiTree. Since we (ideally) have only one profile for any person (no one has their own tree here, there is just one tree), GEDCOMpare would help you determine if the person already exists in WikiTree. Chances are parents/grandparents may not already be here but the further back you go the more likely it is that they may already be in WikiTree (and hopefully a lot of ancestors you didn't before know about).
As to your Questions:
1. Does Wikitree ONLY import family members for whom there are citations on Ancestry.com. No, the GEDCOMpare process will import anyone in your GEDCOM that you tell the system to import (there are certain restrictions for example you can't import someone born before 1700, etc.). If there aren't citations in the import, you'll have to agree in the process to go back and add them.
2. Does Wikitree start with me, moving back in time, and stop importing when there is a break in citations that are supplied in Ancestry. No, WikiTree through the GEDCOMpare process will import (with certain restrictions) what you tell it to import.
Does that help?