Modifying Xenforo compared to IP.board and Woltlab

I'm investigating Xenforo, IP.board, and Wotlab and like a lot of things about each one. I have realized that extendability is extremely important.

One of the things I want to do is to write an extension that creates a link that would create a new thread in a specifric sub-forum with a specific pre-filled subject header and ideally it has pre-filled body text as well. How easy is this to do in Xenforo and can it be done at all? Could you possibly recommend any links on info about modifying and extended your software.
thanks I will look into that. Would that be an add-on that already exists or would I need to write it myself. I know PHP, but am unfamiliar with java and jquery. What sort of obstacles would that give me in writing add-ons like the one I described?