If you haven't fully tested your app with the 100 individual accounts Apple allows you to test via TestFlight or Hockey, then I'd suggest you should test thoroughly with your email list before launching to the app store.

Things to look for at this early-stage:

Activation and Breakage Points: From app download to user onboarding, where are people getting lost? Your goal is not only to have them download the app, but complete whatever steps for them to become your user. Optimizing the flow to ensure maximum conversion is a key first step.

Engagement: How often are they completing the tasks you deem most important based on your business model? How can you increase this number?

User Understanding: How clear is the app's UI and messaging? Where are they getting lost?

Virality: While true virality is hard to measure at this stage (given the constraints of pre-launch testing), you can evaluate the potential effectiveness of any distribution tactics you might employ (contacts, OAuth's etc) in terms of user opt-in and conversion issues.

Real analytical data is easier to interpret than user interviews but there is a such a treasure trove of good customer development intel from customer interviews. Those first 100 people who download the app should be personally interviewed about their experience, what they like, how much it solves their problem, how much of a problem that is for them in the first place and so on.

Before you go live in the app store, I highly recommend you max out your installs in a private testing environment.

I'm happy to talk this through with you in more detail in a call.