Mandarin Chinese is the most frequently spoken Chinese language or dialect with more than 900 million native speakers.
The Chinese characters are more or less the same all over China, apart from the fact that there are traditional and simplified characters and that Cantonese or Hokkein for example have some characters of their own.
There are more than 100,000 or even 200,000 Chinese characters, all variants and defunct included. For reading newspapers you need to know up to 3,000 in Mainland China and 5,200 in Taiwan and HK. For reading high literature, classical Chinese and and scientific texts you may need to know a little bit more, passively.
Some Chinese Unicode fonts have more than 22,000 characters traditional and simplified Chinese included and still won’t meet all your needs, when it comes to very rare characters such as Biang the fantasy character of a Chinese noodle vendor 𰻞 (trad.) or 𰻝 (simpl.), or zhé
a character with 4 traditional long dragons 龍 (lóng), each with 16 strokes, meaning talkative or so.