Qur'an

In addition to praying for assistance in learning, I would suggest that perhaps you can try different techniques for learning. For instance, some people memorize well if they memorize to a fixed set of sounds (such as copying someone's recitation from a recording and always reciting it the same way until it is fully memorized). Others memorize well if they visualize the contents of the text well. Some people even use hand gestures with meanings to help with memorizing.

Personally, I find that knowing more about the tafsir of ayat helps me to remember them better, since I am able to put them in place better and understand how they relate to each other.

I heard of someone once who memorized the whole Qur'an during advertisements on TV. He used to sit and watch the news and then, every day during the advertisements, memorize an ayah or two. So sometimes having small habits during the day to practice can also be helpful, in addition to longer sessions. 

I also find that if I wish to remember something, repeating it while I am doing something else (walking, cooking, etc) helps me to review it in such a way that it is remembered better, because it needs to come out while I am distracted and not focusing on it. Inshallah this is not disrespectful to the Qur'an, but just suggesting it as a possibility.

I am sure there are also other techniques.

I am sure you will get more suggestions from others, but I just thought I would share those.

Also to repeat what you already know daily or as often as possible helps.

Sometimes the challenge with remembering is just due to age, since children are blessed to remember almost everything they see and hear, alas, this capacity sometimes wanes with age while at the same time we grow more busy and our minds full of many other things. So this is another reason to try new techniques. Inshallah Allah will help.

No, insofar as there is not full agreement on the reliability of all hadith about commentary of the Qur'an that has been attributed to the Prophet (S) and Ahl al-Bayt (A). Probably, some of it is correct and some of it is incorrect. Also, we have probably lost a lot of material over history. This is apart from the fact that Shi'i tafsir, in particular, has not been translated extensively into English.

So you will still need to read various sources and investigate and put things together if you want to try to get as accurate a picture as possible. However, some suggestions in the meantime are:

* Read The Study Qur'an, ed. S. H. Nasr, and look specifically at the views from Shii commentators (the names of the commentators are given in parentheses). Of course there is no reason why Sunni commentators should not also have correct views sometimes, but I am just specifying this to give the best answer to the question here.
* Tafsir al-Ayyashi, trans. Nazmina Dhanji, which was just published.
* Reading the section on narrations in Tafsir al-Mizan (some of which is available online)
* Inshallah, ICAS Press is also planning to publish the translation of Tafsir al-Asfa soon, which is also heavily narration based and from a Shi'i lens.

Hope that helps! Maybe some people will also add some good sources.

Some Shi'i scholars have accepted the idea of deletion or rearrangement of material from the Qur'an based on narrations.

Some Sunni narrations also discuss deletions of material in the Qur'an, so it is not a Shi'i-only subject. 

Most Shi'i scholars today reject those narrations and reject the idea of tahrif in the Qur'an. You can find a good argument and overview of the narrations and the subject in https://www.al-islam.org/al-bayan-fi-tafsir-al-quran-prolegomena-quran-s...

This can be a very sensitive and taboo subject because it is generally taken as a primary pillar and fundamental belief of Islam that nothing in the Qur'an has ever been changed (apart from the minor variations in qira'at).

Shi'is are also particularly sensitive because they feel defensive because they feel they have to "prove" to Sunnis that they have the same Qur'an. (And, in fact, Shi'is do use the same Qur'an and same recitations as Sunnis.)

However perhaps it's good to step down from the ideologically and sectarianly charged nature of this discussion and just take it as it is. If some people held this view, it was their view, and that is that. 

According to some scholars in Iran, reiki is permissible.

In order to do reiki properly according to conventional methods, one does not recite anything except for a few words (which are optional and related to the technique), so reciting Qur'an here is not a factor. If one is relying on recitation of Qur'an or something else as the primary method, it is no longer reiki.

Of course there is no harm in reciting Qur'an or playing it in the background, and there is no harm in reciting Qur'an in the hope of or with the intent of healing.