Release Strategy- PO

Hi in release strategy with classification in PO, we have net order value, purchasing group and doc type as the characteristics.

We have two release strategies for PO Z1, Z2.

We have 3 purchasing groups .

Where do we define that system should apply Z1 for Group1, Z2 for Group 2.

Also when Group 3 user created the PO , do release strategy applied this PO?

Also keeping the same config. if i defined third Strategy Z3 , but didnt mention Group 3 for the same strategy, do system apply this Z3 to Group 3 automatically.

Regards, Venu