Is licking the breasts and kissing considered Zina (fornication/adultery) that necessitates the Hadd (prescribed punishment)? And what is the ruling on minor Zina?

What you have done is Islamically forbidden, and it is a minor form of adultery, due to Allah Almighty’s prohibition of approaching adultery. This does not necessitate a prescribed punishment (hadd) because there was no penetration. However, it is very serious, for Al-Tabarani and Al-Bayhaqi narrated that the Prophet, peace and blessings be upon him, said: “For one of you to be stabbed in his head with an iron needle is better for him than that he should touch a woman who is not lawful for him.” You are not liable for a prescribed punishment (hadd) for what you have done, but you must repent, regret, seek forgiveness, conceal yourself with Allah’s concealment, and never return to such an act.