Is there a size limit on where the center channel will have to fit?
I noticed you said the main tower speakers 17 feet apart, but it looks like you will be sitting only 13 feet from the TV, since the room is 14 feet deep. Generally you want an equilateral triangle between you and the main speakers, so I would plan to move them a bit closer together. Also, by your drawing, the in ceiling surrounds are way out to the side. I would also move them closer.
Another piece of advice, avoid a center channel with rear ports, since it will be stuffed in a cabinet. I was going to recommend the Emptek speakers, but their center is rear ported.
You could look at the Aperion Intimus 5T towers and 5C center. They offer no risk in home trial with free shipping. I have not heard them personally, but the brand is well liked.
As far as in ceiling surrounds, there are so many to choose from. I put a link below to a Polk model from Crutchfield.com that allows you to aim the tweeter. Other might have better recommendations.
Finally, as far as 2 zone receivers go, keep this in mind. Some, like the Denon 1712 have two zones but no preouts for zone two. That means that you could hook up one extra set of speakers in another zone if you do only 5.1 in the main zone and the Denon would have to power those with its internal amps. You cannot expand anymore after that. If you look at the 2112 model(link below), it also has preouts for zone 2. That means you can add an external amp and power as many speakers as you need. Much more expandable, and still a good deal on the price. So, you could have two speakers in your living room, two in your dining room, and two outside and control it all from the Denon. All you would need is a multi channel amp.
Total price of the three Aperion speakers' the two Polks, and the 2112 AVR is $1700.
For a sub, you could do the energy s10.3, BIC PL-200, Lava LSP12, or Premier Acoustics PA 120, among others.
Finally, I saw these posted on another thread. Great deal on the price.