Interesting idea, but are you counting on the pillar for some kind of convective heating? I suppose it could work, but I'd be a little worried. When I first assembled my wooden box system (http://www.silentpcreview.com/forums/viewtopic.php?f=14&t=61400
) the fan I was going to use in the bottom of the case broke, so I had the system running without the bottom fan for a bit, just the gpu fans and the cpu and backpanel fans were going. I thought this would be ok for a little bit, and temps got up into the 80s under heavy load, but that was ok. Once I put bottom fans in, cpu temps dropped into the 50s. I suppose with that fan in the middle, you should be ok, but I would definitely start with fans on the heat sinks before trying to go passive. But the components here are much lower power than mine, so you may not have as much of an issue.
But there are some other concerns here as well. ces brought up the power routing, definitely something to think about, you'll need to leave some room to route between your sections. If you set it up right, you can route most of the power lines right along the same wall as the motherboard.
That brings up another issue, how are you going to actually put the components in there? Will one or two sides open up? Are you getting a motherboard tray for the motherboard? The ports don't really need it, but the video card may need some support above the board. Come to think of it, how are cables connected to the board going to get hooked up? You could go wireless for many of them, but you may want a usb connection someplace on the outside you can access, and you'll need cables for video and power, at the very least. And don't forget power buttons and leds, always useful to have those someplace handy. The floorplan doesn't look too bad, but consider the details too, they can bite you in the ass.