An ethnie only actually needs ancestor worship and race worship, since those reinforce the rational side of ethnonationalism.

The terrestrial worship is insufficient, there must also be an equal regard for what is above. There's no disputing that star worship is rational, conferring a sense of proportion. Or as Himmler declared in a speech, "He must once again look with deep reverence into this world. Then he will acquire the right sense of proportion about what is above us".

In Against the Galileans, Julian argued that it had been natural for the ancient societies, without exception, to embrace star worship. Similar sentiment can also be read in Thomas Paine's Age of Reason. They both declare that the original worship consists of contemplating reality, which Julian deemed as a "freedom from passion" and Goethe characterized as a "freedom from fear". In Wilhelm Meister's Travels, Goethe relates that the primitive regard for what is above was the prerequisite for revering what is below, the earthly life.

The explanation was that the stars remained eternally fixed in their circuit, perfect and unchanging as the laws of nature. This actually laid the foundation for Hitler's struggle principle: "a universe in which planets and suns follow their orbits, where moons and planets trace their destined paths" (Mein Kampf). Celsus and Plotinos noted that the omission of reverence for the stars was peculiar to later generations of Jewish-Christians.

Anything else, like morality, needs to be grounded in pure reason to avoid its discarding in the event that the 'religion' itself is discarded by some foolish generation at a later time.

A conception of right (part of a Weltanschauung, or view of life) must be grounded in idealism. "Pure" reason is a Kantian fiction. Schopenhauer points out that the intellect is merely a tool devoid of content. Hitler denounced the intellect as "a mere external phenomenon without inner value."

As many safeguards need to be added to the new social order to ensure that no such unraveling occurs, e.g., explicitly racial constitutions or other foundational documents of the new society.

That's approximating the cynical thinking of the Catholic Church and Soviet Union, that the masses cannot think for themselves and must be protected from conflicting truths.

It should be assumed that future generations will quite rapidly seek to undo whatever it is that we achieve... We should assume that the next generations will be total idiots as these preceding ones have been, who will squander everything, and continue from this worst case scenario.

That's a faulty premise to start from. NeoRail has already sufficiently addressed how, logically, this line of reasoning leads to the employment of coercive methods. More specifically, the formation of a priestly caste, which has always counteracted the desired goal.

This is why the Burkean social contract is superior to the Rousseauian social contract.

The same Rousseau who turned to ancient Sparta as his model for rebuilding Western civilization and who laid down the best indictments for democracy and liberalism?

Schopenhauer would've been revolted by how Edmund Burke reduced the principle of religion to a system where god exclusively functions as a paymaster, dishing out reward and punishment. In a letter, Thomas Jefferson expressed his disgust for how Edmund Burke had mingled his seemingly virtuous actions with repulsive motives (as evidenced from Burke's Reflections on the French Revolution).

Just reconstruct an explicitly racialist Paganism complete with the kind of ancestor worship...

Jefferson wrote a treatise comparing Jesus' doctrines with the ancients, in which he noted that they had cultivated a regard for the country, family, and friends, but fell short of social benevolence. Apollonios of Tyana drew attention to how compared to humans, the sparrows practiced social benevolence. Goethe indicated that Christianity, after it had been purged of its defects, ought to become the final religion since it had helped usher in the rehabiliation of the criminal element.

It should be noted that Jefferson was regarded by the eugenicist Hans F. K. Guenther as one of the last genuine Indo-Europeans.

Lastly, religions that place great emphasis upon souls have the potential for great harm, simply because they are an obvious pathway to egalitarian nonsense like 'judge by the content of one's character (i.e. mind or soul) and not by colour (i.e. body or gene)'.

Stoicism, which places such emphasis, remained the only stabilizing edifice in ancient Greece. In Marcus Aurelius' Meditations, he acknowledges the importance of the racial aspect, but also lays stress on the mental link between humans: "What links one human being to all humans: not (common) blood, or birth (seed), but mind. And... that an individual’s mind is God and of God."

Basically, a more physicalist worldview is required (I'm a physicalist-leaning dualist, moving ever-further in the physicalist direction, far away from the kind of metaphysical idealism of the likes of Berkeley or Kastrup, that Keith Woods has dangerously entertained).

Physicalism (the view that only physical matter/ physical world exists) is an errant life view, it has nothing to do with a world view conception. Most Christians are physicalists. Their "spiritual world" has nothing to do with Materialism (world view) since it's the only other world which exists for them. Originally, Materialism was the acceptance of innumerable worlds (Demokritos, Epicurus). Why did Jefferson embrace the Epicureans while rejecting the Platonists?

Indeed, I call for a new culture rather than a new religion per se.

Your proposition actually has very little to do with culture (whatever exerts an ennobling effect on a people's development, whether in the arts or science), but remains tethered to basic necessities of civilization (history, literature, laws, politics, etc.).