1- Hurmat-ul Musaharah happens when a non-Mahram man and woman touch each other sexually while the bare skin of one touches the other's. There are other details of this chapter as well which can not be explained through this answer.
Once Hurmat-ul Musaharah is established then the mother, grand mother, etc,,, and daughter, grand daughter etc... will become Haram for the man forever. Likewise, the man's father, grand father, son, grand son etc... will also become Haram for the woman to marry.
2- It is not true that those who could not repay debts in the time of the Holy Prophet Sallallahu Wa Sallam were made into slaves/ concubines. Slaves were only those people who were born as slaves or captured as slaves.
It would not be permissible to turn a free man/woman into a slave. It is a sin of great caliber.
3- I did not understand the term "Nikah e Misyar". Therefore, I am unable to provide an answer.
4- Islam only allows and believes in permanent marriage. When someone marries a woman then the purpose of marriage should be to maintain the marriage to the best of one's ability.
Islam does not allow, nor believe in temporary marrieages. All forms of temporary marriage is prohibited under Islamic law. Furthermore, if a time limit was stipulated during the terms of Nikah then the Nikah would also stand invalid.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America