This thread is huge so I will go ahead and ask these two questions:
1. Can one rig use two different miners at the same time? For example if I have mixed nVidia and AMD cards on one rig, I'd like to set ccminer to mine lets say ravencoin and the AMD cards to mine ETH. Is this possible?
2. I suppose the rigs would need to have windows installed on them. Is it possible to boot them from USB without the need of a hard drive?
If your motherboard supports it, you could run windows from a usb drive, BUT, there is an issue with mining where you need to set your pagefile size to the size of all the memory on your graphics cards added together, which depending on your hardware could be quite large (my main rig has 1080tis for example so the pagefile size if I had all 6 cards would need to be 66 GB) I could imagine the usb bus speed being a bottleneck also, so I wouldn't really suggest it. What I would suggest from a performance standpoint is the fastest SSD you can find. I got the one I'm using for $52 on Amazon though it's only 120GB. If I had to do it over again (I guess it's not too late) I'd get 2 of them and use one just for the pagefile, though it would be an experiment, I think it would be superior, and if it didn't offer a solid performance gain, you could always just use it for the next system it was needed for.