Does the .ttf actually have Chinese characters in it? I have noticed that some fonts might not work, but in your case try to see if just a couple of characters work first and then go from there. I don’t think there is a character limit although I don’t believe we’ve tried thousands of characters, should be fine though.
If it doesn’t work you might want to experiment with a different font. If you want share your problematic font and the characters you need with us so we can have a look.