I have a excellent book "Islamic FActs refuting the allegations against Islam write by Dr. Mahmoud Hamdy Zakzouk. He explain about ur questions. So i will write some of ur question here
Is the Islamic code of punishment brutal?
1- Islam is not a religion that advocates brutality. On the contrary it calls for mercy, clemency, and toleration. Nevertheless, it insists on establishing law and order in the community so as to safeguard the freedom and the rights of its members, and to protect their lives, beliefs, wealth, possessions, and families. When Islam imposes a certain punishment for a specific sin, it takes into consideration two factors:
a) Man is not infallible, but it constantly exposed to temptation. Thus the door of repentance is always open to those who regret having committed sins and repent and desire to atone.
b) Every member of the community is entitled to live a life of safety and to feel that he, his family, and his property are not exposed to any kind of danger. Thus the depraved or corrupted behavior of criminals should be dealt with accordingly, so that the peace-loving members of the community would not live in a state of fear and apprehension.
2- Although Islam had made laws to punish crimes, it requires decisive proof of the guilt of the accused person before passing a sentence on him and does not enforce the punishment if there is any doubt concerning his guilt. Also if any guilty person repents sincerely of his sin, the sentence can be suspended if the judge is convinced of the sincerity of the accused. The Prophet said: ��Try to prevent enforcing the penalty on Muslims whenever it is possible to do so, and should there be the slightest doubt as to the guilt of the accused person, set him free. It is far better that a judge errs in remitting the penalty than erring in enforcing it. �
Such an authentic saying from the traditions of the Prophet is the essence of mercy and tolerance.
3- The penalty for adultery in Islam depends on a certain condition that makes it almost impossible to enforce. The condition is that the act of adultery must be witnessed by four peoples who must swear that they saw the act committed. Accordingly, the two incidents in the history of Islam when this penalty was enforced were the result of the confession of the guilty parties and not of the evidence of witnesses. The Prophet did his best to try and persuade the guilty persons to change their statements in which they confessed their guilt but they confirmed them and the Prophet was accordingly compelled to order enforcing the penalty, in spite of his profound grief. In view of the condition stipulated and the extreme difficulty of fulfilling it, such a punishment never occurred again in the history of Islam.
Also you have to know that It only for the married couple who do zina with other person. Also you have to know that if other persons. And anyone who have a penalty for his sins like zina on earth, he will not be punish on the Day of Judgment since he allready being punish for it on reath, he will be saved from that.
I will continue writting about cut off the hand and the femal circumission later inshaAllah take care