Crossfire in mining, dont use. It will actually slow it down.

As for the powered risors it should be ok to run 2x cards on one strand. This will not be the only thing powering the card. Its just to make up for the smaller amount of power that would normally come from the motherboard. Its the 8pin or 6pin connectors that you want to come from differnet strands.

Also:
1. you may need to make dummy plugs to mimic monitors
2. you may need to jumper wire the pcie 1x to get it to work. (I had to)

Its totaly possible to still make money with asic, just not mining bitcoin. There are other coins and if you get that amount of hardware you are looking at likely 6gh and thats about $1/day