we shall be in Paris for 5 days and live near Metro station Gabriel-Pery. If we buy a metro 5-day pass, how many zones do we need?

By default the Navigo Decouverte pass includes all five zones in and around Paris metropolitan area.  You can no longer purchase Navigo passes that only include central Paris say Zones 1-2.
A single Paris Metro ticket price from Gabriel-Peri to anywhere on the Metro system will cost 2.80€.