Conditions for the validity of Nikaah

Q: If a lady marries a man on a condition that he will not take a second wife and he agrees, will the nikaah be valid? 

Q: Regarding nikah witnesses on Ask Imam website it states:

The wakeel represents the bride in the presence of the two witnesses who must be trustworthy and pious male Muslims. They should not be from among the girls ascendants e.g. father, etc. nor from her descendants, e.g. son, etc. https://islamqa.org/hanafi/askimam/28924

Could you please explain the above regarding witnesses in the nikaah. Will the nikaah be valid if the witnesses of the nikaah are among the girls ascendants e.g. father, etc. or from her descendants, e.g. son, etc?

Q: I was told that a divorce in court is like a talaaq. There is no need for a separate talaaq. However if you make nikaah, is that valid or does one have to separately get married in court?

Q: My sister's name is Aay Bee but during the nikaah ceremony the Mufti said "Aay Khan" instead of "Aay Bee". I just want to ask if this nikaah is valid or do we need to do the nikaah again?

Q: I have done a civil marriage with a non Muslim girl who will convert to Islam, but has not yet converted due to some financial problem. I have tried to get the nikaah registered but they are asking +/- 10,000 for registering and certificate. Now I have one child. Kindly assist on how to get the nikaah properly and how can I correct my mistakes.

Q: I want to marry a second wife, do I need permission from my first wife?

Q: In a nikah ceremony for a new Muslim couple, one male adult wakeel on behalf of bride and another male adult witness were present. Is the nikah for both valid. Later this nikah was register in a madressa with a mufti.

Q: Can you let me know in Islam if a nikaah is only valid if it is performed by an imam and if there are witnesses present? Or is the nikaah valid without being performed by an imam and without witnesses or can the couple perform nikaah themselves?

Q: Is it necessary for a man to seek permission or even to bring to the notice of his first wife about his second marriage? I know its after effects but I just want to know as per shariah if it is necessary or required?

Q: I am a Muslim but my boyfriend is Hindu. He is going to convert to Islam and then we will get married. My question is that after accepting Islam, he wants to keep his culture the way it was. For example, he wants to have a wedding according to the Hindu culture. Is it permissible for him to keep his Hindu culture?

Also, I am willing to turn vegetarian because he was brought up as a vegetarian. Is it permissible for me to do this?