Question 1:
Would this be overkill in terms of wattage? Perhaps I can save $50 and go with two 1000w? And how should I connect everything up.. 4 cards on one psu and the system + 2 cards on the other?


My Answer:
I use 1000W on mobo and 3 GPU, power draw of ~850 watts, then 6 GPU on a 1250W psu. I would say stick to name brand, 1000W+, PSU's thats been my only issue so far. I cannot recommend the Corsair RM1000 enough, that thing is a beast, plus the cabling it comes with is amazing.

Question 2:
I've heard of people linking power supplies together so they get turned on at the same time, how do I do this and is this necessary? What do they mean by "do not mix" when doing this.

Answer:
http://aphnetworks.com/lounge/turn_on_psu_without_motherboard_the_paperclip_trick

Turn on the non-mobo connected PSU first, then turn on mobo. works flawlessly.

Question 3:
I have 6 USB powered risers.. some of the posts I've read from people make me nervous about this whole power concept. But my plan now is to connect the two molex on the motherboard up, as well as connect all six powered risers to each card. I guess I'm concerned about frying the motherboard or the cards.

Answer:
I have the two molex on mobo plugged in, as well as all my risers plugged in. Been running safely for ~3 weeks now.