I want to write a letter daily to Imam Mehdi as to obtain a physical bond with Imam but I don't have any water body to flow it and I can't think of a place where I can bury it. So, please give me examples of places where I can bury it and what I can do to make it reach Imam Daily.?

You can send salam to your Imam (as) and address him directly.

Why are we allowed to kill animals for our consumptions? Since animals feel sadness and we are omnivores why not just consume plants and vegetables? Here is the article I saw regarding animal emotions.

https://academic.oup.com/bioscience/article/50/10/861/233998

One of the purposes Allah created them for is consumption.

Is wudhu in toilets valid? (If it is the only place where one can find water for example). Of course not in the toilet in itself but in the space/room of toilet

Wudhu is valid with pure water.

I want to know how come Imam Ali lived his Life in Kufa and passed away in Kufa but Imam’s shrine is in Najaf. Who took Imam’s body to najaf?

Kufa is part of Najaf. They are joined to each other

Please can you explain if the Quranic Surahs were revealed as single ayats or they were revealed as full surats consisting of multiple ayats.
I trying to understand if the surahs compiled later on by combining different ayats during compilation of Quran.

It happened in both ways.

I have recently come to know that backbiting count as a sin only when talking behind a muslim. So when talking behind the back of a non muslim will it not be a sin? Is it atleast makruh?

Even though this may be relating to believers specifically in another perspective it would not be morally good to talk bad about others even if they are non Muslims.

What was the age of Imam Ali when he first started offering namaz?
I've heard from our islamic scholar that he was around 9 years of age and others have criticised him

I have not read of a specific age

I recently came across this sermon from Nahjulbalagha and it states that Imam Ali said that Prophet Muhammad had prevented them from wailing and mourning. Why do we mourn then?

Wailing is recommended for Imam Hussain (as) in many narrations.

When we have a loss in our lives we remember and mourn Imam.
I highly recommend this book

Commemorating the Mourning Rights of Imam al-Husayn https://smile.amazon.com/dp/1514298619/ref=cm_sw_r_cp_api_glt_fabc_25H7R9JH0X7R70JBFGW6

https://youtu.be/Fdt19d8E90Q

If we've been directed to seek help and protection from Allah only then why do we say Ya Ali Madad or similiar to this.
Even in Nahjulbalagha Imam Ali A.S says do not ask for help from anyone except Allah in Nahjulbalagha letter no. 31?

Allah is the ultimate source of the need being solved but using a waseela (means) is recommended. See Quran 5:35

Does chicken and turkey have to be slaughtered a specific way for it to be halal? Or is that just for animals like lamb, cows, etc

Yes it needs to be slaughtered with the proper conditions to make it halal.

See: https://imam-us.org/wp-content/uploads/2019/03/Islamic-Rulings-of-Food-and-Drink-Published-by-IMAM.pdf