How does Disarming Assault interact with the Multiple Attack Penalty?

A barbarian has picked up the Disarming Assault feat. He uses it as hit first action.

1. Does the Strike increase his Multiple Attack Penalty?
2. If the Strike increases his Multiple Attack Penalty, does the Athlectics check to Disarm suffer the increased Multiple Attack Penalty?
3. Does the Athlectics check to Disarm increase his Multiple Attack Penalty?
4. What is his total Multiple Attack Penalty after using Disarming Assault?