I have been searching around, but all the sources give completely different answers ranging from 2,000 to 50,000. So my question is how many Kanji characters that have ever existed since the dawn of time? Does this include unofficial characters?
An authoritative classic, the Kāngxī dictionary, lists over 47,000 characters. The Hanyu Da Zidian, a more modern reference, has over 54,000 characters; the Dai Kan-Wa Jiten, the Japanese equivalent, has over 50,000. Even more recently, the Zhōnghuá Zìhǎi has over 85,000 characters, but apparently many of those are variants.
Of course, such counting is more-or-less academic. In Japan, there are only 2,136 Jōyō kanji (lit. commonly-used kanji), which are the ones taught in school, though literate people usually know more. The equivalent list in Chinese is the Xiàndài Hànyǔ Chángyòng Zìbiǎo, which has about 3,500 characters.
50,000 is usually the number given for the number of Kanji characters since the dawn of time.
2,000 is roughly the number than comprises compulsory education.
5,000 is often assigned to particularly well-read persons (e.g. university professors).
I remember reading a newspaper article about one of these "living national treasures", who was supposedly able to read 10,000 characters. (I have yet to find a reference.) One does have to wonder, however, how they determined the number.