2) Should I worry about matching manufacturers and models? In my experience RAM is quite fickle about these sort of things in that matching it as closely as possible could determine how well it performs. Again, this is solely while crossfire and eyefinity are enabled.
uhm no, doesn't really matter. They all have GDDR5, and its the GPU itself that communicates via PCI-E to the CPU, not the Vram.
3) When/if I go to crossfire the two GPUs, should I also split the displays between the two? Have one GPU running the 2 sides while the main is handled by the other.
When you use Eyefinity all Monitors have to be connected to One GPU! also Games in Crossfire mostly use
AFR So you cant choose which GPU renders what.