1. Yes, so the one I just did last night, the 6 holes at the bottom were fine, the three across the middle I had to drill two hole, and the top three holes are floating in space at the moment because of the layout of the case I have. (better to get the Elysium BaBa)
To do the holes, I mark the spot with the mobo in, then take a metal drill that just fits into the existing mobo holes and drill out the spots, then because I am cheap and don't have a tap and because I want it to be a tight fit, I take an old case thumbscrew with the pointy end (old coolermaster stainless screw) and use that to roll tap a hole, the mobo mounts then screw right in nice and tight.
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But yes you might have to build something to mount the top three holes to that are floating in air in most cases.
As I said to teabag the most important bit is that you have 12cm of mobo *ABOVE* the i/o ports area. So for cases its important to find one with room in the roof.
2. Memory, I know that they perform better with 4 banks per cpu filled so finding one that can take cheaper DDR3 that isn't ECC or Registered is important. The supermicro's are good for that, the Tyans need the more expensive server memory.
But you could get 16 x 1GB DDR3 if you wanted
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I've got 2GB Corsair XMS3 Classics
3. Any 850W+ Quality brand PSU would be fine, total from the wall is around 660W while folding, running a 875W one here. Obviously if you got one with gpus you would need to take that into account, but for bigadv folding you don't need silly gpus
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