Well, for the orks it seems like much of the game would be based on terrain placement, so as to allow good bottlenecking, or to impede flanking.
Termies would be excellent for this. They would cut through the orks like a hot knife through butter.
Ya, you definetly wanna be careful against the DE anti-tank. very nasty stuff...
How many tanks do you plan on feilding, in, say, 1500 pts?