Welcome!

As Aska has mentioned, you can bypass the 1000-character per post restriction by simply posting a few lines, then going back and editing the rest into the post immediately after. As far as I can tell it's an attempt to try and prevent or limit spamming of the forum.

Also be aware that there are other posting restrictions on the forum as well, such as the amount of posts and threads you can make per day, the details of which can be found in this official thread.