Let's start with "Sono sicuro" >> I am sure. "Sono sicuro di questa cosa" >> I am sure about this (thing). So: sicuro di = sure about. Then we take phrase "I am sure about this" and say "I am sure about it". Word order in Italian: "about it I am sure" >> NE sono sicuro. About is = ne.
I don't agree with your explanation. I think that despite your step by step explanation seems to be logical, the conclusion is actually wrong. The "ne" stands in place of " it" and is not related with "about". The "ne" refers to the thing which you are sure about, and the "about" is just a preposition needed in English to express your security is related to something else. That "something else", the thing you're sure about, is an object, a grammatical object that is represented by a PRONOUN, a word that stands in the place of a noun, that some-thing.
While in English you need the preposition ("about") to express that you're not only just sure but specifically sure about something, that's an English issue, other languages may need another proposition or no preposition at all.
In Italian, on one hand that something is present in the sentence, with its own syntactic function, represented by the pronoun "ne", so ne=it/that/that-some-thing. While on the other hand the "di" is a preposition needed by "essere sicuro", just a "credere" may need "in" or "a" (for credere in una cosa, like "credo in mio capo" when you beleive IN him); or credere a qualcuno like "credo al mio capo" when you believe WHAT he says).
So "About" is just an English's preposition needed to articulate the action of being sure with the thing you're sure about, and while it may partially coincide with the Italian preposition "di" in some translations and in that it articulates the act of "essere sicuro" with the thing you're sure about, that's just an accidental coincidence and "about" is not always nor most times "di", and that rather depends on the verb.
That thing which the "ne" explicitly refers to something whithout naming it. In a prepositional language, the preposition independently stands for the thing usually without any preposition being needed, while the preposition is actualy in concordance with the verb: as about is related to "to be sure", and as "di" is related to "essere sicuro", and as "to" is related to "related" for something to "be related to another thing", as "by" is related to "to go" in "to go by train", and "for" or "against" to "to be" for you to "be for" or "be against something", and in this manner each verb uses a determined set of prepositions in a way of its own in each language. So the preposition depends on the verb, while the pronoun "ne" stands in its own right for the thing (the grammatical object) you're referring to without naming it, that still holds its syntactical place in the sentence, represented by a word that is there replacing the noun (the pronoun) in a pronominal language.
It may sound weird for a not-so-pronominal-language native speaker, like an English one, but it is completely natural for a Portuguese and specially for a Spanish native speaker as those romance languages tends to "abuse" of pronouns in their sentences like Italian does, being common to combine even two of them in a single sentence.
Here's some more info on "ne" : http://italian.about.com/library/fare/blfare167a.htm
In Italian, the pronoun ne can mean "about," "any," "some," "of it," "of them," from it," from them," or "from there." It can also replace a prepositional phrase beginning with da or di. Here are a few examples:
Parliamo di Mario. (We talk about Mario.) Ne parliamo. (We talk about him.) Hai bisogno di due francobolli. (You need two stamps.) Ne hai bisogno di tre. (You need three of them.) Avete molti amici. (You have many friends.) Ne avete molti. (You have many of them.) Ho due fratelli. (I have two brothers.) Ne ho due. (I have two of them.)
You are absolutely correct! Actually, they come from the same source, Classical Latin "inde" with the same meaning and function. "Inde" turned into "enne" through assimilation (the process of facilitating pronunciation), the French took the first part and the Italians the second! See http://www.etimo.it/?term=ne
Yes, but the thing that is sure is you, a singular thing.
Ex. Sono sicuro(a) che ho caduto le mie chiavi sotto la scrivania. Ne sono sicuro. (of it I am sure)
Ti piacciono i nuovi operai al tuo lavoro? - Non ne sono sicuro(a), aspetterò e decidere quando lavoriamo insieme. (I am not sure of them)
At least, this is my understanding. I wish a native speaker would clarify...