Hi,
If you don't have Unity 3.x Pro, I would definitely wait and get Unity 4 pro, now you can always get the Unity 3.5 free edition and start with this.
I don't think PlayMaker officialy support Unity 4 but it does work yes. I would in all cases simply get the open beta for Unity 4 and test.
I don't know if a new license for playmaker will be required for Unity 4.
bye,
Jean