Generally speaking, Muslim scholars state that a Muslim should avoid Tankees (inversion) in the current order of verses in the Mushaf, and it makes no difference whether the verse recited first is the long one or not. As for the Tankees in Surahs, Muslim scholars state that it is not tawqeefi (i.e. known to be absolute as dictated by the Prophet himself), and hence one is permitted to resort to inversion in Surahs.

Dearest brother, the whole issue you referred to in the first part of your question is known as Tankees in recitation, and to have a comprehensive view about the whole issue we would like to furnish you with the following comprehensive fatwa issued by Sheikh Muhammad Saleh Al-Munnajid, a prominent Saudi scholar, in which he states the following:

Reading later parts of the Qur’an before earlier ones is called Tankees (inversion). There are different types of Tankees:
Tankees Al-Huruf (inversion of letters)
Tankees Al-Kalimat (inversion of words)
Tankees Al-Ayat (inversion of verses)
Tankees Al-Suwar (inversion of chapters)
Tankees Al-Huruf means putting a letter before another in the same word; for example, instead of saying “Rabb” one reads “Barr”.
Undoubtedly this is absolutely Haram (prohibited), and invalidates one’s prayer, because it changes the Qur’an from the way it was revealed by Allah, and usually alters the meaning in a drastic manner. (Ibn `Uthaymeen, Ash-Sharh Al-Mumti, vol. 3, p. 110)
Tankees Al-Kalimat means putting a later word before a previous one; for example, instead of saying “Qul huwa Allahu ahad”, one reads “Ahad Allah huwa qul”. This is also Haram, no doubt, because it changes the Qur’an from the way it was revealed by Allah. (Ibid. p. 110)
Tankees Al-Ayat means reciting a later verse before a previous one; for example, reciting “min sharr il-waswas il-khannas” before “ilah il-nas”.
Concerning this, Al-Qadi `Eyad (may Allah bless his soul) states: “There is no dispute concerning the order of the verses in each chapter of the Qur’an. This is something Tawqeefi, i.e., based on revelation and is not open to Ijtihad (personal reasoning) and the order is that which now appears in the Mus-haf, and this is how the Ummah transmitted it from the Prophet (peace and blessings be upon him(. (Sharh al-Nawawi, 6/62; this was also the view of Ibn Al-`Arabi, as stated in Al-Fath, 2/257)
Shaykh Ibn `Uthaymeen states: Tankees Al-Ayat is also Haram according to the most correct view, because the order of the verses is Tawqeefi, which means is that it was dictated by the order of the Prophet (peace and blessings be upon him). (Ash-Sharh Al-Mufmti’, 3/110)
Tankees As-Suwar means, reciting later chapters before earlier ones; for example, reciting Al `Imran (second chapter of the Qur’an) before Al-Baqarah (second chapter of the Qur’an).
the scholars who do not agree that orderly arrangement of Surahs in the Qur’an is Tawqeefi do not see anything wrong with such Tankees. However, those who maintain that the order of Surahs is Tawqeefi or that the consensus of the Sahabah (Prophet’s Companions) on the order of Surahs is evidence, say it’s not permissible.
The preferred view is that the order of Surahs is not Tawqeefi; it is the result of Ijtihad on the part of some of the Sahabah. There was no Ijma` (consensus) among the Sahabah on the order of Surahs; the order in the Mus-haf of `Abdu-Allah Ibn Mas`ud – for example – is different from that in the Mus-hafs of others.
In the Sunnah there is evidence that supports the view that Tankees As-Suwar is permissible. Here are some Hadiths:
1. Hudhayfah (may Allah be pleased with him) narrated: I prayed with the Prophet (peace and blessings be upon him) one night, and he started to recite Surat Al-Baqarah. I thought he would do Ruku` (bowing) on reaching one hundred verses, but he kept going. I thought, he would finish the Surah in one Rak`ah, but he kept going. I thought he would do Ruku` then, but he started reciting Surat An-Nisa’, and he recited it all, then moving to Surat Al `Imran and recited all of it…” (Narrated by Muslim, 772)
this Hadith indicates that Surat An-Nisa’ was recited before Surat Al `Imran. An-Nawawi quoted Al-Qadi `Eyad as saying: This is an evidence to support the view of those who say that the order of Surahs is the result of Ijtihad on the part of the Muslims when they wrote down the Mus-haf. The Prophet (peace and blessings be upon him) did not dictate the order of Surahs; he entrusted this task to his Ummah after his death. This is the view of Malik and the majority of jurists, and it is one preferred by Al-Qadi Abu Bakr Al-Baqillani, who said: It is the most correct of the two views, although both are possible.
an-Nawawi adds: What we say is that following the order the Surahs are placed in the Qur’an is not binding when writing, praying, studying, teaching or learning. There is no report from the Prophet (peace and blessings be upon him) to make a deviation from that a forbidden act. Hence, the order of Surahs in the various Mus-hafs differed, before the Mus-haf of `Uthman. The Prophet (peace and blessings be upon him) and the Ummah after him in all ages regarded it as permissible to differ from the order of Surahs in prayer, and when studying and teaching.
however, according to An-Nawawi, the scholars who say that (the order of Surahs) was dictated by the Prophet (peace and blessings be upon him) and that he put them in the same order as appears in the Mus-haf of `Uthman, interpret the fact that he (peace and blessings be upon him) recited Surat An-Nisa’ first and then Al `Imran as meaning that this happened before the final ruling was dictated, and these two Surahs appear in this order in the Mus-haf of Ubayy.
he said: There is no dispute concerning the fact that a person who is praying may recite in the second Rak`ah a Surah which comes before the Surah which he recited in the first Rak`ah; but it is Makruh (blameworthy) to do this in one Rak`ah, or when reciting the Qur’an outside of Salah but some scholars permitted this.
the view of Salaf (righteous predecessors), prohibiting the act of reading the Qur’an in an inversed order, is interpreted as referring to those who read from the end of a Surah to the beginning.
al-Sindi states: The phrase [in the Hadith of Hudhayfah] “then he started to recite SuratAl `Imran” means that it is not obligatory to follow the order of Surahs when reciting. (Sharh An-Nasa’i, 3/226).
2. It is reported on the authority of Anas Ibn Malik (may Allah be pleased with him) that a man from amongst the Ansar (Helpers) used to lead them in prayer in the mosque of Quba’. Every time he led the prayer, he would start his recitation with “Qul huwa Allahu ahad” (Surah no. 112), then when he finished it, he would recite another Surah. He would do that in each Rak`ah. On being confronted by his companions on this, he said, “I am not going to stop doing that. If you like, I will lead you in prayer as I have been doing, and if you do not like it, I will leave you.” They preferred keeping him, as they saw him one of the best of them, and they did not want anyone else to lead them in prayer. When the Prophet (peace and blessings be upon him) came to them, they told him about this. He said, “O so and so, what is stop
ping you from doing what your companions tell you? What makes you keep on reciting this Surah in each Rak`ah?”
“I love it,” the man replied. The Prophet said, “Your love for it will grant you admittance to Paradise.” (Narrated by Al-Bukhari and At-Tirmidhi)
the evidence in this report is the fact that the man recited Surat Al-Ikhlas in his prayer before any other Surah that comes before it (in the Mus-haf), and the Prophet (peace and blessings be upon him) approved of it.
3. This was the action of `Umar (may Allah be pleased with him). Imam Al-Bukhari narrated: Al-Ahnaf recited Surat Al-Kahf in the first Rak`ah and Yusuf or Yunus in the second, and he said that he had prayed Fajr with `Umar and he had done the same. (Kitab Al-Adhan, chapter of Al-Jam’ bayna Suratayn fi’l-Rak’ah).”

Finally, we would like to say that we are so sorry for not being able to answer the other questions you pasted because of our tough schedule and the rains of questions pouring on us daily. You are kindly advised to submit it as well as the other question you want one by one and we will answer them all, in sha’ Allah. Please appreciate our attitude and keep in touch!