{∅, {∅}, {∅, {∅}}} : Rage Against the Meat Grinder

He did heartily recommend Kant,Plato,Upanishads and Puranas.

This is true.  I do not take those recommendations lightly.  One thing leads to another and we really do only have so much "time" or even "attention".  It certainly requires some discipline and a bit of stubborness to focus in on anything in particular. 

Like you, I would eventually wish to revisit Kant with the intention of better undertanding just why Schopenhauer was so impressed.  When I had been reading Kant, I noticed every now and then I would notice a separate "life of the mind" developing.

Maybe we will live long enough to give the Upanishads and Puranas the attention they deserve and most likely require.

As for Plato,  I am currently following his intstructions as far as,  "Let none ignorant of geometry enter my door.”    It is a branch of mathematics which has never really grabbed me, but for whatever reason, I am currently very strict with myself in that I seem not to be allowing myself to explore the other texts in my "personal library" (a personal temple of sorts) until I work through the exercises of two giant geometry texts which I had very carefully chosen.

You see, my ignorance of geometry had become unacceptable to me.

Rather than going for the current "geometry software," I have enjoyed learning to use the straightedge and compass, doing the work in a kind of sketchpad reserved for "artists".  I am no artist, so drawing red lines and blue circles is a kind of "arts and crafts" experience for me.

Books on computational physics beckon me, but I remain determined to cover even things like "construction" which do not seem to have any "purpose" in our world other than as a mental exercise.

I did a little search to find out some opinions about why Construction is taught.  you see, one textbook from 1993/2000 had a section on "Construction and Loci" whereas the more current one from 2011 did not.

In this thread, I found there was much disagreement, but I was impressed with the following short response:

The beauty of straightedge and compass constructions, as opposed to the use of, say, a protractor, is that you don't measure anything. With ruler and compass you can bisect an angle without knowing its size, whereas with a protractor, you would have to measure the angle and then calculate the result.

In other words, the point of this form of geometry is that it can be done independently of calculations and numbers.

As you may know, I tend to favor (or be stronger in) the use of algebra, arithmetic, and numerical calculations using algorithms - so, I am not necessarily focusing on what I like, but focusing on those areas where I feel I am weak or ignorant.

I suppose the only reason I do not feel ignorant about Kant is only because I trust that, through Schopenhauer, I may have received the best of what Kant was trying to communicate in a way that I would not have understood were I had focused prinmarily on the translations of Kant (as Schopenhauer suggests we do).

I had read that even some native German speakers/readers prefer the English translations - for whatever reasons, mostly having to do with the way Kant wrote.

Schopenhauer recommends Plato, and yet Plato demands we not be ignorant of Geometry; so, in a round about way, by decreasing my ignorance of Geometry, I am following Plato, and thereby following Schopenhauer's recommendation.  (in a round about way, of course)

These subjects would be well suited for a man locked in a tower like de Sade was.

I read that he was aloowed to have his wife drop off many books for his own personal jailbird library.   De Sade would not have fared so well in "the land of the free".