I think this question decide on how you define fluent is ,and for different people the number is different.If you really need an answer ,I would answer "many".The most important is to learn gradually.So I don't think this question should be found too hard on searching the key.

3000

3000-4000

3 000 or 3 500 are enough for everyday writing, they cover more than 95% presence in general writing. They are what common Chinese write in for daily use. By just these there may be a problem that you hit 2 or 3 characters that you do not know in a 1 000-character essay. The more possible happening is that due to not knowing the certain characters or words which are most suitable for using there, they would not coming into your mind at all. For more professional writing, 7 000 should be enough. 7 000 is not a terrifying number. Remember you have to acquie an English vocabulary of more than 15 000 to write fluently. Chinese characters are constructed from about 200 components----compare it with english 500 roots and suffixes; And, the components are constructed from 5 strokes-------- compare it with the 26 roman letters. The only difference and thus difficulty is that english words are written in line while Chinese characters in plane. The strokes of Chinese characters have different: separate, parallel, or intersecting, planar relationaships with each other to make components, and components make characters in the same way. But the figures of all the components have their respective meanings. They are presenting their meanings by the images---- structure. To find out how the images express their meanings is a very interesting job. Once you make it out you'll have not to labor on memorizing the structure, but find it a great pleasure. Components make up characters and add new meaning......... The sound of characters are also systematic and easy to memorize.....................