You can reveal any number of events from the top 10 cards - all of them, or just one, or none at all. You don't need to place any events in the discard pile if you don't want to - it's not a drawback, it's mostly for synergy with The Annals of Castle Black and recurring events (e.g. The Prince's Plan).
- Placing cards in the discard pile does not trigger any "When/After a card is discarded" abilities (e.g. Crone of Vaes Dothrak, Tywin Lannister (LoCR)).