I think there is no other way to copy something to the clipboard automatically or at least I found no other way when I was making
Chat2Clipboard.
The character limit also seems to be something we cannot work around (zgoo has the same limitation when you copy the list).
I haven't tested it myself, but I think the only way to copy more than 900 characters is to let the user copy the text by himself.
Try to call SetMaxInputChars and set it to something like 10000, add some long text and then see what happens if you call ctrl+a and ctrl+c manually.