Regarding (1), ZZ is [hold shift][type zz][release shift], while :x is [hold shift][type :][release shift][type x], so I'd say :x is 1 more action than ZZ, and

Regarding (1), ZZ is [hold shift][type zz][release shift], while :x is [hold shift][type :][release shift][type x], so I'd say :x is 1 more action than ZZ, and the timing of the release makes it slower IMO.