I wouldn't assume that your app goes viral by default. In fact the chances of this happening are very slim. The guys that made breakup notifier almost went off the new page when they went viral.

What I would do is put it out there and be ready to take the steps you need to, to keep it alive if it does go viral. Planning too far ahead for this is probably a waste of your time as you most likely wont be able to see the weak points before hand. Just move quickly if it does.