Why didn't Nabi (sallallahu alaihi wasallam) go into the details of sihr?

Q: I know that learning sihr is not allowed in Islam but what is the ruling on learning about sihr? There is a ruqya course on YouTube whose ustadh has an ijaza in the 6 books of hadiths and is an experienced raaqi but he goes into a lot of details on the kufrs the magician commits, how sihr is performed, and tells the meanings of the numbers in taweez and how the magicians use numbers to calculate the taweez. He has also read actual magic books (e.g. Shams al ma'arif, etc. for "informational" purposes maybe). We also come to know that the magicians say the name, "Baal" and blow on the knots. Even the footage of an actual magician is shown when he was being exposed. If this was allowed, why didn't the prophet (sallallahu alaihi wasallam) go into so many details? And of course, he tells us how to destroy the taweez and perform ruqya. I find it very iman boosting as it shows that Islam is the truth but am I sinning by watching these videos?

Taking precautionary health measures in moderation

Q: Is it a misunderstanding of Islam to refuse to go beyond using pure supplications to Allah in order to overcome a huge problem at hand? Some local imams are prescribing things like taking special baths and drinking certain concoctions in addition to supplications and azkar. These are good and devoted imams. They say that it's okay so long as one is not committing shirk or using something forbidden. But I am not so sure. Moreover, I am someone who naturally believes in and prefers pure supplications, especially Quraanic and Prophetic supplications.

Please I NEED you to confirm the truth on this matter.

Duration of one alif in tajweed

Q:

1. What is the duration of one alif in tajweed? How long should we stretch it?

2. I have seen in ‘simple rules of tajweed’ book that short madd duration is two alif. Can I stretch short madd for 3 Alif duration?

3. If sign of the short madd appears at the end of an ayat and we stop there, how long should the madd be stretched? I have heard in many tilawat that they stretch it for one alif when it appears at the end of ayat.

Shar'ee mile in kilometers

Q: Please explain how many kilometers are equal to 1 shar'ee meel (mile). It is mentioned in Beheshti Zewer under the ruling of tayammum. Generally in length; 1 mile = 1.6 km. Is there any diifernce between a shar'ee mile or and English mile? If yes please explain.