bobbay

As has been said, it can be done, but it isn't optimal. An 8x8 AMS is like 1600 bucks. This is not nothing, but in the entire project, is it that much more to avoid any pitfalls? You can add all 5 streams from a Core5 plus three other audio devices if needed, and avoid any issues with grouping zones etc. I dont think you can get 5 streams of tidal or spotify or pandora to play the same thing in sync this way. Especially the digital to dac to amp zone. Bite the bullet and get the AMS

Binary MOIP will definitely work over Cat5e. With 4k Roku or Apple TV. But, MOIP still uses pretty aggressive compression to make it all work, so your onscreen PQ won't be as good as  an HDMI matrix or even HDBT matrix. Whether it is visible to you is another story.

Don't use C4 Video Matrix. Use AVPro Edge if doing a matrix. Game consoles won't work centralized, no way for the handheld controllers to connect to the console from any distance.
Shields, Rokus behind TVs and audio fed back to Audio matrix saves a ton of $$ on video distribution. 
Many ways to skin this cat, but good video distribution will blow your budget right off the abt.

The Contemporary dimmers/switches are NOT decora. They are smaller. They will fit in a Decora faceplate, but there will be gaps around the device. C4 Contemporary faceplates will NOT work with standard decora outlets, switches etc. The opening is smaller than a Decora opening. There is or is going to be, a C4 faceplate that is 1 contemporary opening and 1 decora opening. 

But the Epsons aren't 4k projectors are they? 1080 chip with pixel shift? The Sony and JVC are native 4k chipsets. 

Sony 950H or 95J if you can't get the 950H still. Sony over Samsung All day every day. 

Use Roku Ultras for your video sources. Flawless IP control with C4, direct app access etc. Also half ish  the cost of Apple TV. Apple TVs are only reliable with IR control and lack direct app access etc. Not sure what you mean by the ads on a Roku. I push Netflix/Prime?Hulu etc on my C4 remote and launch directly to those apps, hardly ever see the Roku menu. Don't use built in apps on TVs except in rooms you rarely use .  Video over IP becomes fairly close in cost to matrixes over 8x8. But flexibility and scale are a win. Figure 1k per source and 1k per display at least for Just Add Power Binary Moip etc. Plus the POE switches and network infrastructure. If using C4 for control, use C4 lighting. If this is a new construction use panelized, especially for this large a house. For shades you can use Lutron still with a RA2 select hun as interface, or Qmotion with native Zigbee, or Screen Innovations. Wire for power if you can and control if possible. If you want the TV audio over the distributed system, you will need to bring audio back from the TV if usoing local sources to an audio matrix then to the amps. If all central, video matrix/voip audio extracted to audio matrix. Use Zektor audio matrixes. C4 can integrate with Honeywell, DSC and a few other security panels. Carrier infinity will be separate.