Amina Inloes

It's not prohibited to celebrate things during the first 10 days of Muharram, but it is better not to celebrate out of respect for Imam Husayn.

If one considers it necessary to celebrate something (for instance, a wedding of a relative who is not Muslim), it is good to be moderate and more serious during the celebrations or spend a limited amount of time on celebrations, rather than being extremely celebratory.

However, these are not requirements; rather, it is simply a matter of respect and honoring the seriousness days. Generally, people who do commemorate the martyrdom of Imam Husayn over the first 10 days of Muharram do not want to engage in celebrations, anyway. But it is understandable that life happens, and sometimes other things occur during these days.

So it is your own decision.

It is very bad form to have celebrations on Ashura itself, and I personally would avoid that not only out of respect for Imam Husayn, but out of fear of divine displeasure.

In some Sunni-majority regions, for historical reasons, it is customary to celebrate Ashura in a happy way as a holiday, and while I find that deeply distasteful, I do understand that this is their history and custom and they are honoring it in the way they are used to honoring it, and are not intending any disrespect towards him.

Here are some differences between Sunni and Twelver Shi'i practices during Ramadan and Eid.

Ramadan:
* Shi'is usually fast a bit longer than Sunnis because the maghrib time is about 15 minutes later. Fajr time may vary slightly too. Usually Shi'is stop fasting slightly before fajr to be careful (the time is called imsak).
* Shi'is commemorate the main nights of laylat al-qadr on the 19th, 21st, and 23rd. There are specific du'as and acts of worship for these nights which you can find on duas.org. On the 19th to 21st, the martyrdom of Imam Ali is commemorated.
* There are also some other du'as which may be recited during the month of Ramadan which you can find on duas.org.
* Shi'is do not say taraweeh prayers in congregation; however, in some places, people get together for reciting the Qur'an so the whole Qur'an can be recited in one month. Otherwise it is good to do it individually.

Eid
* Eid is celebrated on one day rather than 3 days
* Shi'is also celebrate Eid al-Ghadir and other days such as the birthdays of the Prophet and Imams
* There are some differences in the Eid prayers including the qunut which is sometimes confusing (you can look it up)

Maybe there are some other differences which some others can mention. However most of these are for optional things (like reciting dua) and not requirements, apart from the fasting times. 

Best wishes!

Tuhaf al-'Uqul: "He who begins his day thinking of something other than God is not one of the people of God. He who does not care for the affairs of the believers is not one of them. He who succumbs to humility is not with us; the Prophet’s family."

وقال صلى الله عليه وآله: من أصبح من أمتي وهمته غير الله فليس من الله. ومن لم يهتم بأمور المؤمنين فليس منهم. ومن أقر بالذل طائعا فليس منا أهل البيت

It means someone who willingly agrees to be humiliated or disgraced, for instance, those who sold themselves out to tyrants such as Yazid in exchange for money or material benefits, even though they knew it was wrong. 

Humbleness, in the sense of not being egotistical or arrogant, is a good quality ethically.

However, it is also good to have a balance - it is good to be humble as long as people are respectful, but if they start stepping on you or taking advantage of you, then it is good to assert yourself politely.

Of course, a believer is always humble towards Allah. 

Yes

Yes

In Twelver Shi'i fiqh, it is generally considered unlawful to eat lobsters or crabs. Shrimp/prawns are allowed because there are hadith from the Imams (A) specifically permitting them.

Among the Sunni schools of thought, most of the madhhabs allow eating lobsters and crabs, but the Hanafi school of thought does not allow eating them. 

There are a lot of reasons why someone might be having suicidal thoughts, and if there is no obvious reason why you are feeling this way (such as grief or loss), it is worth considering that there could be physical causes such as heavy metal poisoning. I would recommend seeking out medical or psychiatric assistance and seeing if they can help. 

With duas!

Yes, they can follow Shi'a Islam regardless of their parentage, ancestral religion, or age. 

Sunni hadith may be considered on a case by case basis regarding their authenticity.

"If there was a prophet after me, it would be 'Umar" - Sunni scholars have disagreed regarding the authenticity of this narration. Some Sunni scholars have considered it authentic, whereas others consider it weak and reject it. Shi'i scholars do not accept it. 

This question is somewhat vague (for instance, what is "true nature" and "commonly understood"), but I'll give it a go.

As a general rule, the way that things outside the immediate material realm work are somewhat different from what is commonly understood, because we as people have difficulty grasping them. (In fact, we as people also have difficulty grasping things that are very large or very small, even in the material world.) So with respect to the way these things work, what is commonly understood (or even ever understood by the vast majority of people) is lacking.

There are some videos on YouTube,  etc, these days, by Muslims (usually, Salafis) claiming to talk about how black magic is done, signs of black magic, etc. These videos are true in some ways and not true in other ways. So it is best to be skeptical about them, or not watch them at all. 

In al-Kafi, it is related that Imam al-Sadiq said that the Prophet said: "Recite the Qur'an according to the tones and sounds of the Arabs. Beware of using melodies belonging to people who transgress or commit misdeeds. For, after me, different peoples will chant the Qur'an in a singing and cooing fashion. The monks' incantations are also not allowed for it, for their hearts are facing the wrong way, as are the hearts of those who admire them." 

So this is the general idea of maqamat, which are the traditional musical modes of the Arabs, although not exactly mentioning maqamat in detail.

http://shiaonlinelibrary.com/%D8%A7%D9%84%D9%83%D8%AA%D8%A8/1123_%D8%A7%...

Anything that occurs depends on the permission of Allah. 

As for whether the Imams can exert control over the natural world, through the permission of Allah, within Shi'ism, there are varying views. Some scholars hold that they have the capability to affect the natural world in any way. Others say they have this ability in special cases where a supranatural act (karamat) is called for. Still others reject this idea as heterodox (ghuluww). 

I personally hold the first view.