I agree with Jason, I think either the VP-100 or 150 will work fine in your room.
In regard to vertical vs. horizontal centers, we are all trying to help you find the optimal solution for your room. I had a horizontal center for the past many years. After much research I recently decided to experiment with an M2 as a vertical center instead of my VP150 ( see this thread
) . Long story short, I preferred the M2. So based on the lesson I learned, I would tell anyone to try a vertical center if possible before they commit to a horizontal center. Now, if a vertical simply won't fit then there is no point discussing it and you should just move on to the VP series. Just wanted to clarify where we were coming from on the center channel discussion.
For the L&R side surrounds I believe you really will appreciate the QS series sound dispersion over the direct radiators. No opinion from me for the back surrounds I can see how either might work.
Good luck and keep us posted on what you decide to do.