Cu exhibit +1 oxidation state more frequently because Cu^+

is stable with completely filled d orbital

 

 

in lower oxdation state, some of the valence electrons are not involved in bonding so ENC will not be high. after the formation of oxide, it is ready to donate electrons but those oxides with higher oxidation state, all the electrons would have been involved in bonding so the oxides with high ENC has the tendency to gain electrons so acidic in nature