When to Create/Update/Delegate Spotlight index for app with Core Data

Question

I have an app where user create items backed by Core Data. I want to start adopting Spotlight search and index all the items. What is the right approach for this?

For new user I think I can rely on willSave to add/update/delete search index, but for existing user I need to have a bulk index all of the items. I think I will do it in on first launch.

Is this a right approach to do index?