Offering congratulations for `Eid should come after the `Eid prayer. But if one offers such congratulations before the `Eid begins, to be the first to give this greeting to his friend, it seems that there is nothing wrong with that.

If you reach the place of the `Eid prayer while the Imam is delivering the Khutbah, you should listen to the Khutbah, then you should make up the `Eid prayer after that.

The Sunnah acts and etiquettes of ‘Eid include: 1. Making ghusl before ‘Eid prayer. 2. Eating before going out to pray on ‘Eid al-Fitr and after the prayer on ‘Eid al-Adha. 3. Takbir on the day of ‘Eid 4. Offering congratulations 5. Adorning oneself on the occasion of ‘Eid. 6. Going to the prayer by one route and returning by another.

We do not know of any report speaking of the virtue of the `Eid prayer that mentions a specific reward; rather it is included in the general texts mentioned above and others.