Can (and should) I use Ask Ubuntu to ask a question that I already know the answer to in order to make a "how-to"?
Sure. Just come up with a good question, and put the howto in an answer. We're here to answer real questions, but we don't have to personally have the problem in order to present it.
Just remember that posting your howto means you're putting under the cc-wiki with attribution license (see site footer).