Firstly wish to point out that the first verse quoted, has to do with retaliation. As for the second it specifies the punishment for the crime committed. Furthermore the hand is not amputated if someone for example steals a pencil, or an orange. Rather it is cut off when someone steals something of great value.
A thief's hand was not cut off for stealing something cheaper than a
Hajafa or a Turs (two kinds of shields), each of which was worth a
As for death for those who commit adultery and are married, the punishment is stoning to death
You free to not accept Islam if you do not wish to, but if you do it is a serious things, and it is not allowed to come in thinking that you can leave or come it try it for a while then leave, no, if you enter Islam, enter with knowledge. The punishment for leaving Islam is Death, and the reason this came about was when the Jews of Madinah started entering Islam in groups and at the end of the day leave to deter people away from accepting The Truth, The Prophet (peace and blessings be upon him) ordered those who leave Islam to be killed.
مَنْ بَدَّلَ دِينَهُ فَاقْتُلُوهُ
He who changes his religion kill him
After that, how many jews do you think pretended to be Muslims the next day?
So yes, those who leave Islam are to be killed, period. And there is no compulsion in the acceptance of religion, so if you do not want to accept Islam then that is you choice and cannot be forced. Also it is worth mentioning that the death punishment is not acted upon until the authorities have argued, and sought the reason, and try to convince he/she not to leave Islam. Also, the death punishment is acted upon by the authorities, and not by some individual Muslim.
Lastly I would like to point out that, the point of these punishments being prescribed for these crimes, is to deter people from committing them. I end with that, and I ask Allah to guide us all.