Hi,
All of this is completly doable with playmaker as is, not need to think about building custom actions. You need to first make sure you are confortable with the following in playmaker.
1: can you work with prefabs?
2: can you instanciate a prefab in the scene
3: do you know how to work with triggers
4: do you know how to control gameObjects ( for the seeking)
5: do you know how to play a sound?
This would be your first step, learn all the above points. For any of these, let us know if you have questions or issues, and we will assist.
Bye,
Jean