Since the world is going into the Dark Ages, I would like to suggest a path of learning to sustain civilization for the small remnant.
The Written and Oral Law of Moses. [Which means  mainly the two Talmuds but also includes other books that contain the basic oral law it was all written down. That  midrashim of law (Sifrei Sifra etc), and midrash that are agada. The reason I bring Rav Shach's Avi Ezri is that is provides a way to understand how to learn the Oral Law in depth.]
Also Physics and metaphysics.

I hope that the basic idea is clear. I am talking about learning fast--saying the words and going on until you have finished the two Talmuds. That is Gemara with every Tosphot and Maharsha. The Yerushalmi with the two side commentaries Pnei Moshe and Karban Eda.
Plus the same with Physics and Metaphysics.
[That means Physics up until and including String Theory and Math which means mainly Algebraic Geometry and Algebraic Topology.] [Metaphysics means Plato, Aristotle, Kant, Hegel, Leonard Nelson.]
[Rav Avraham Abulafia, from the Middle Ages seems very important, but I have not had a chance to study his works thoroughly so I am hesitant to recommend what I am not that familiar with. See Moshe Idel's books of Abulafia. One aspect of Rav Abulafia that I find fascinating is his positive approach towards Jesus, and yet I have not really had the chance to go into the issue in detail. The basic idea seems similar to how you consider the Patriarchs, Moses, Aaron, Joseph, David. I.e., souls of Emanation.

Fix bayonets. You will be forcibly removed from your home and family. Negative tests mean nothing.

https://www.barnhardt.biz/2020/04/07/fix-bayonets-you-will-be-forcibly-removed-from-your-home-and-family-negative-tests-mean-nothing/

To approach God is thought to be by spiritual things -not by Physics and Mathematics.

And to some degree you see this in later achronim [authors after Rav Yoseph Karo] like The Paths of the Just. 

However this does not look like the opinion of Ibn Pakuda [author of The Obligations of the Hearts] nor other rishonim [mediaeval authorities] that followed the path of Saadia Gaon.

And the reason seems plain and simple. That Physics and Math deal with the wisdom of God that is at the core of Creation. 

That is where you see the glory and wisdom of God.

But in the world of ethics, and morals and spirituality you see things are messy. That even morality is subject to people's opinion seems to be thought to be  a desirable thing. So fine. If so, then fine,-- but that does not make it objective and revealing God's wisdom.

[You see this in the Gemara where God said one thing, and the yeshiva in Heaven said something else; and they said 'a certain amora would decide between them''. And also in the events with R Yehoshua that in Bava Metzia the law goes like the majority opinion because "the Torah is not in Heaven". [However the issue is that to get to God's deeper wisdom in the work of Creation, one needs to learn and keep the Laws as they apply to people in order to get there.]

So you can see why in the parable of the palace in Guide why the Physicts are put into the palace of the King and the people that learn and keep the Oral and Written Law ("talmudiim) outside.

[The parable is in the Guide for the Perplexed. There you have  a king who rules in a country and there are levels of closeness to the king. People outside the country, those inside, those close to teh palace, and those inside the palace. In that parable those who keep the whole Torah perfectly are outside the palace. Those who learn Physics are inside.] 

[The most practical way to do this is to have a few books of Math and Physics and go through them in order from beginning to end--in order. As you see in Rav Nahman's Conversations  section 76. Say the words and go on. But to do this you need faith and trust in God that He will help you understand what you think you do not understand.]

תוספות הר''יד קידושין דף ג Rav Shach explains the Tosphot HaRi''d

The basic idea of the תוספות הר''יד  is that חליפין would work to acquire a wife if the handkerchief has a פרוטה worth. His point is the only thing the גמרא really means to exclude is קניין חליפין when one of the objects being exchanged is less than a פרוטה. This is why רב שך is dividing between two kinds of exchange in order to answer for the תוספות הר''יד. If it has a פרוטה's worth, then it comes under the category of acquiring by means of money. Only when the handkerchief is less is it actually קניין סודר היינו מטפחת which would not acquire a woman. This answers my question I asked yesterday that the גמרא is holds חליפין does not acquire a woman, and does not mention קניין סודר היינו מטפחת. My point today is that קניין סודר  in the view of the תוספות הר''יד is a kind of חליפין, but even חליפין is OK if it is more than a פרוטה. And that is the way רב שך answers the questions on the תוספות הר''יד

רב שך ברמב''ם הלכות אישות פרק א' הלכה ג' מביא את תוספות הרי''ד שקניין סודר תקף אם שווי המטפחת יותר מפרוטה. כמו כן, תקף אם ניתן בתנאי לתת מאוחר יותר מנה כסף, ובהמשך הזמן הוא נותן את זה. רב שך מסביר שיש שני סוגים של קניין סודר, האחד הוא חליפין, והשני הוא סוג מיוחד של חליפין שקיים רק כסוג של דרך להשלים עסקה. כמו בימינו לחיצת יד תהיה בקטגוריה מסוג זה. אז התוספות הרי''ד כולל בקניין כסף קניין סודר כאשר זה נעשה כחליפין ללא שום התחייבות נוספת לתת דבר נוסף. וזה יהיה סוג של חילופי כספים שווה בשווה ולא כשזה נעשה במיוחד כמו קניין סודר שהוא קטגוריה משלו (של סוג חילופין). שאלה, הגמרא מעוניינת בעיקר לסלק את קניין חליפין, ולא מזכירה קניין סודר. רק כדי שיהיה ברור אני אביא את הגמרא הבסיסי. הגמרא קידושין מביא משנה בשלשה דרכים אישה נקנית בכסף שטר ובאיה, וזה נועד להוציא את חליפין. שיכול להיות שהייתה לומד חליפין משדה עפרון, מכיוון שחליפין יכול לקנות שדה. אז אנו יודעים כעת לא, מכיוון שאישה לא תסכים שיקנה אותה בפחות מפרוטה. ומכיוון שחליפין יכולה להיות עבור פחות מפרוטה, לכן כל הסוג של קניית חליפין אינו נכלל, אפילו אם החליפין נעשה יותר מפרוטה .השאלה שלי. הגמרא מעוניין להוציא את סוג הרכישה שהוא חליפין ספציפית, ואפילו לא מזכיר את קניין סודר. זה נראה בדיוק ההפך ממה שאמרנו למעלה. זה נראה כאילו קניין חליפין לא יהיה תקפה, אבל אולי קניין סודר רגיל יהיה תקף.

הרעיון הבסיסי של התוספות הר''יד הוא שחליפין תפעל לרכישת אישה אם ערך המטפחת  יותר מערך פרוטה. הנקודה שלו היא הדבר היחיד שגמרא באמת מתכוון להוציא הוא קניין חליפין כאשר אחד החפצים המוחלפים הוא פחות מפרוטה. זו הסיבה שרב שך מחלק בין שני סוגים של חילופים כדי לענות עבור התוספות הר''יד. אם יש לו ערך פרוטה אז זה נכלל בקטגוריה של רכישה באמצעות כסף. רק כאשר המטפחת פחותה מפרוטה, זה בעצם קניין סודר היינו מטפחת שלא היה קונה אישה. זה עונה על שאלתי שהגמרא מחזיקה חליפין לא רוכש אישה, ולא מזכיר את קניין סודר היינו מטפחת. הנקודה שלי שקניין סודר בתוספות הר''יד הוא סוג של חליפין, אבל אפילו חליפין זה בסדר אם זה יותר מפרוטה. וככה רב שך עונה על שאלות על התוספות הר''יד.

Now Rav Shach explains the Tosphot HaRi''d that if the handkerchief is more than a pruta/penny the acquiring of the wife is valid. But it looks at that that might not be so to the Rambam. On one hand the Rambam says in three ways a woman is acquired, money, sex or a document. The Mishna says the same thing and the Gemara itself says that the Mishna is meaning to exclude a handkerchief. However  after Rav Shach makes clear there are two kinds of acquiring by handkerchief. One is when the handkerchief is meant to accomplish more than just the handkerchief. Like as the Ri''d says along with it he says he will give another amount of money. But by itself it is simple barter.
This opens the possibility if perhaps the Ramabm would agree with the Tosphot HaR''id inthe same case. But why would he? because in laws on Buying and Selling he says barter does not have a law of overcharging. That law says if one overcharges more than a 1/5 the sell is null. The Rambam brings from the Rif that that law does not apply to barter because this one wanted a needle and that one wanted a suit of armor. But the Rambam says that law does apply to fruit with fruit. That means barter would come under the category of  a sell by money.  So that would apply to marrying a woman also. So the handkerchief --if more than a penny-is an act of acquiring by money, not barter.

Rac Shach does not actually say all this but it is clearly what he is implying as raising this possibility. But also he brings the case of letting a slave go tat he says does not work if that was done by handkerchief. . There he makes no difference. So perhaps marriage is the same.

The basic idea of the Tospfot R"id [Rav Isaiah, one of the baali Hatospfot] is that barter would work to acquire a wife if the handkerchief has a penny's worth. His point is: the only thing the Gemara really means to exclude is exchange when one of the objects being exchanged is less than a penny.

This is why Rav Shach is dividing between two kinds of exchange in order to answer for the Tospfot R''id. If it has a penny's worth then it comes under the category of acquiring by means of money. Only when the handkerchief is less is it actually kinyan Sudar which would not acquire a woman.

This answers my question I asked yesterday that the Gemara is interested in eliminating exchange and does not mention kinyan sudar (acquire by exchange of a  handkerchief).

My point today is that kinyan sudar in the view of the Tosfot R''id is in fact a kind of exchange but even exchange is ok if it is more than a penny.
And that is in fact the way Rav Shach answers the questions of the Tospfot R''id

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The known calendar seems to be based on Meton from Athens, and was not mentioned in the gemara. Nor is there anywhere mentioned in the Gemara that Hillel II sanctified the calendar.

I think Passover ought to be on the 15th day after the new moon. That is,- if you think of the day of the "molad" [when the moon and sun are joined at the same longitude], as the new moon, then 15 days from that ought to be Passover. But why think this? Mainly because of Tosphot in Sanhedrin page 10 side b at the top.
The known calendar seems to be based on Meton from Athens, and was not mentioned in the gemara. Nor is there anywhere mentioned in the Gemara that Hillel II sanctified the calendar. That is thought to be the case, but in fact it is no where in Shas.
There are in fact many examples of basic things in the Gemara that people are not aware of.
[One more reason to get through Shas yourself.]