Monitor dummy plugs:
I want to run my two rigs with 4x 5850 cards each without any external I/O. Do I NEED at least one monitor to keep them running?
Or do I just need one monitor to boot up?
Or do I even need 8 dummy plugs for each card? Can those be bought or must they be built by myself?
A computer does not need a screen to be connected to start up.
Two rigs, one account? How do I mine with two rigs to the same wallet file? Or won't it matter if I just have two wallets and simply split everything?
It is suggested to use the same Bitcoin Address for all your pool work (this means it'll be the same wallet of course).
Graphic card compatibility: Are there any graphic cards that won't fit on the MSI GD70 boards - like physically not fitting next to each other because they are too high?
Can I mix up cards from different labels, like 2 Sapphire, 1 Asus and one XFX?
You can try, but it's generally saver to use crossfire, due to bios or driver problems that might arise otherwise, and running several different cards is generally a very rarely used approach, so finding support (online or official) would be limited too.