Hi Maritza
Both question 1 and 2 has a similar answer: I am not sure whether you can do that with Work Center hierarchy nut during your trials, you must make sure to update the "Evaluation Paths" configuration in order to cover the work centre hierarchy.
Now the other option you can use and I have tried was using teams. So you can use a tema in stead of using a higher level of work centre:
Teams - SAP Multiresource Scheduling - SAP Library
Teams are more flexible then hierarchies as you can easily arrange new teams etc.
I hope this helps.
Savas