How would you leverage a big list of email subscribers that you can also segment depending on their interests?

All users are mobile users and I can segment them based on apps they like or use. My idea was to try to promote different mobile apps to lookalike audiences (via Facebook) based on these interests.

But I still have a couple of questions before I will start testing:

• Are there any better use-cases for this data?
• What would be a good number of a data sample for lookalike audience?
• What kind of margin would you add to the marketing campaign costs in order to keep it relevant for the advertisers?