How could Peter have been the first pope if he was married (see Mark 1:30, and Luke 4:38-39)?
Being married does not preclude one from being head of the universal church. It is technically possible for any Catholic male to be elected pope, although traditionally it has usually been limited to Cardinals. Regarding married priests – even today celibacy is not the rule for all Catholic priests. In fact, for Eastern Rite Catholics, married priests are the norm, just as they are for Orthodox and Oriental Christians.