Assalamu aleykum,
Masturbation is undoubtedly a sin in Islam and it is not permitted in any circumstances.
As this verse of the Holy Qur’an states:
"And those who guard their chastity (i.e. private parts, from illegal sexual acts). Except from their wives or (the captives and slaves) that their right hands possess, - for them, they are free from blame. But whoever seeks beyond that, then those are the transgressors." (23:5-7)
To research further the Islamic view about masturbation and its consequences, please refer to the following texts:

Assalamu aleykum,

There is no hadith that allows to have sexual intercourse before marriage, it is a very wrong assumption. It is undoubtedly forbidden.

Please kindly refer to the book "Marriage and Morals in Islam" by Sayyid Muhammad Rizvi:

https://www.al-islam.org/marriage-and-morals-islam-sayyid-muhammad-rizvi/chapter-three-islamic-sexual-morality-2-its#b-handling-sexual-urge-marriage

Assalamu aleykum,
The main duty of a woman in marriage, the only thing that she cannot deny her husband unless under specific circumstances.

Assalamu aleykum,
Thanks for your question.
These words literally mean: “The hand of Allah is tied up”. It is just a small portion of the verse 5:64 that talks about the Jews making fun of God. 
Please read through these three Commentaries of the Holy Qur’an for further explanations.

Sorry, it is quite a long read.

Assalamu aleykum,
Thanks for your question.
If the son is illegitimate he has no right to inherit, so yes, the will is completely valid.
Please refer at the texts here below.

Assalamu aleykum,
Thanks for your question. 
There is no rulings against performing Hajj, Umra or Ziyarat for a woman accordingly to Shi'a Fiqh, the issue is only about safety. It is not clear what you mean by "a group of other Muslimahs". Do you mean an organized group? 

Assalamu aleykum,

Thanks for your question. 

Examining and doing medical procedures while studying to become a registered nurse or a doctor, being a part of the training required to reach that position is absolutely permitted. 

Kindly refer to the following texts online:

- A Code of Practice For Muslims in the West by Ayatullah Sistani, under the chapter “Medical Issues”, especially question 355 and 356: