Those things which render the Salaah invalid

Q: The problem I face throughout the prayer is that I feel laughter in my chest. I think it comes from fear of breaking prayer due to laughter. There are times when I compulsively (quite intentionally) pronounce letters, especially "haa", mixed with laughter and sometimes, by forgetfulness.

Most of the time, voice cracks continously while reciting and very little part of my voice is audible (due to uncleared throat) and feelings of laughter seem to get mixed. Can you please let me know what is the type of laughter that breaks Namaz? I keep feeling every Namaz is invalid.

Q: My routine in Tahajjud Salaah is to recite daily one juzz from the Quran in a bit of a loud voice from my mobile or I-pad fixed on a stand before me. Please inform me whether this is acceptable as per Islamic rules.

Q: If you think about something funny in salaah, and you don't fully laugh but a small sound is made from the mouth, then are the salaah and the wudhu broken?

Q: How thick may a musallah (prayer mat) be? I bought a thick musallah (prayer mat) and I want to know that when performing sajdah on it, should the head and nose feel the earth or carpet below it (prayer rug) in order for the sajdah to be valid?

Q: Is the prayer of someone who has inserted something into its rectum (to block flatulence) before doing wudhu and removed it after praying valid?

Q:

1. If I use my hand, due to losing balance, when coming up from sajdah, will this break my salaah?

2. Whilst making my niyyah for salaah, at the beginning I scratched my face and then used my one hand twice in salaah. Is this amal-e-katheer?

Q: If one swallows a few strands of coconut during salaah which was stuck in the teeth, will it invalidate the salaah?

Q: Recently, I came across a clip of someone quoting the following hadith and explaining its great virtues:

عن عبد الله بن عمرو بن العاص، قال: قال رسول الله صلى الله عليه وسلم: من قام بعشر آيات لم يكتب من الغافلين، ومن قام بمائة آية كتب من القانتين، ومن قام بألف آية كتب من المقنطرين (سنن ابي داود رقم 1398)

The same person explained further that if one is unable to recite that amount of verses from memory, he may recite them looking inside the Quran Sharif in salaah, be it in nafl or fardh salaah. His argument was the practise of Hazrat Aaisha (radhiyallaahu anha), who would appoint a person by the name of Zakwaan and he would lead her in salaah during the month of Ramadhaan, while reciting from a mushaf.

My questions are:

1. Does this hadith refers to only reciting in salaah or can refer to reciting outside the salaah?

2. Is it permissible to recite looking inside the Quran sharif while in salaah?

3. If is not permissible in the Hanafi mazhab, is there any permissibly for it in the other mazaahib? Under which circumstances will it be permissible (i.e. any difference in the maslah as far as a person who knows some portion of the Quran from memory and who doesn’t know, and any difference between a fardh and nafl salaah)?

4. If a Hanafi performs his salaah behind a person who is reciting looking inside the Quran sharif, will his salaah be valid?

Q: Is it correct that if a person does an action that is not part of Salaah. e.g. scratching the body, etc. for more than 3 tasbeeh, the Salaah is broken?

If one performs Salaah behind someone who does this... Does he have to repeat his Salaah?

Q: What is regarded as Amal-e-katheer in salaah?