I read Stirner's 'The Ego and His Own' through some time ago, and feel certain that Nietzsche must have been aware of it. Controversy rages as to whether Nietzsche deliberately concealed this influence; and if so, why.

Certainly, Stirner's attack on Platonic forms and his recognition of both the death of God, and the need for fluxions [as in the sections you quote], mark him out as a forerunner when you consider that his book was published around the year of Nietzsche's birth.

But Nietzsche was not, like Stirner, purely an individualist. He recognised the great chains of necessity which link beings together, although it is true, one can see in Stirner's vague and undeveloped notion of a union of egoists, something similar to Nietzsche's Free Spirits; but the latter were/are a station on the way towards superhumanity, which in itself is on the way towards...eternal becoming.
Also, of course, Nietzsche affirmed Classical culture, and despised those Anarchists [many of them inspired by Stirner] who sought to destroy without building.

And in purely philosophical terms Stirner does no more with the Ego than assert it. So, while he takes Egoism in a myriad of different directions, he takes the Ego as a 'given'.
Nietzsche, being a more profound philosopher [and psychologist], looks at the very nature of the concept 'ego'. He finds it to be dependent on the old 'soul atomism', and therefore something that must be distrusted as a factitious monad bent on hiding a 'multitude of sins'.

However, I would regard Stirner's book, along with Emerson, Goethe and Schopenhauer, as essential background to contextualising Nietzsche's work.