In an open floor plan like yours, when it comes to picking speakers and subs, you've got to keep in mind the total room area that's open, not just the area you've defined as your home theater. The sound waves have no way of knowing that only the first 30 x 27 is your set aside space for it. It just travels as far as it can until it hits walls and ceilings.
30 x 27 is already a big enough space, coupled with an unknown volume of kitchen space, you've got a challenge to fill the space to SPLs you're happy with.
I'd pick the most efficient speaker I could find, of course, because you're going to need all the volume help you can get for your space.
Now, the next question would be something you may or may not have thought about - what kind of sound from an audio system do you prefer? Edgy? Laid-back? Smooth? Linear? This will play a huge part in picking the speakers to buy.
BTW, the sensitivity (efficiency) of your Paradigm center is 90db in-room, which is kind of middle to low of speaker efficiencies.