It is refreshing to see someone buy used gear and see modern stuff and not tie-on booms

Usually you go with the boom that requires the smallest amount of extension, in order to reduce the amount of flex that the boom has.On the other hand, some people like to leave one boom adjusted for a certain sail, and just use a different boom for each sail.
Yeah, if you clamp it too low or too high, you just release the clamp and reposition it. If it is not tied to the clew, then there will be minimal pressure on the clamp, and you can easily slide it to the new position.
Once you are comfortable with doing this, it is usually possible for people to release the clamp and move it, even when the clew is tied off. I do this often when I sail if I find that I clamped the boom on too high for me, or I want to effectively lengthen my harness lines by raising the boom height.
Just out of interest, what is the other equipment? What sail, mast, and board are you using?