i did not check out the asrock mainboard, but it will work with the msi (and all other mainboards, as long as you have more than one physical pci-e x16 (the long one) slot available). on the msi board you can actually put up to 4 of your mentioned cards! (yeah i know you can use extenders and put even more cards on there, but we are not talking about this
the psu will be enough for 2, maybe 3 cards!
and well, you need a cpu, ram and some other things like mouse and keyboard and maybe a case with some fans
and instead of 2 monitors you could use 1 dummy plug or a kvm switch