I wouldn't make this an English argument. You try to make a distinction for quantity and number and I see those words as synonyms in most contexts, and in all the ways you mention, so it's not really productive.
They are not only quantities, that is what I mean. They are quantities with a condition of "being close to another quantity". They are not exact quantities if you like that term. [...] So if infinity is not a number, I would say that 0.999... is certainly not a number as it is a sum of infinite numbers.