2) Must have separately-vented power supply with enough space for an extra-long modular unit. Bottom mount preferred.
How long a PSU do you need?
I got a good deal on a 550-watt Kingwin Lazer Platinum. It's 170mm deep. And it's probably overkill, but the reviews looked good and the price was right. However, I bought it when I was aiming for a full ATX build, and now it's occurred to me that I'll only have two expansion cards and one SSD, and just might be able to get away with a mATX build instead.
Perhaps you could even go mini ITX and buy a Bitfenix Prodigy which performs very well in regards to thermals. There's room for a big CPU cooler, but there will not be much room to strap on a fan on the Accelero.
I'm definitely stuck with mATX or bigger. I use a fan on my Accelero already, and I'm hoping to use a dedicated sound card as well. I do like your point about well-ventilated cases, though. I certainly don't have any huge noise sources in a system like this. And if I turn out to be completely dissatisfied with my setup, I can always go up to a full ATX case anyway, as long as I'm not making any sacrifices to use the smaller motherboard in the first place.