-They did reference the MWBoS in-game, and Lyons wouldn't have known that the MWBoS had gone rogue unless they made contact with them. As of the end of Tactics, the MwBoS had never made contact with the WCBoS after their crash. Someone, aka Lyons, would have had to go make contact with them to know they had gone rogue, and had not just been unable to make contact for whatever reason.
-Same way the wasteland survival guide made to Vegas in large quantities in only 4 years.... people brought the information with them as they walked across the nation.
-Possibly, but D.C. being the nation's capitol, and having so many military instillations in one spot, makes collecting tech far easier then trying to hunt down all the remote military bases of the deserts of western America, since its all jam packed into one small area.
The mutants are in D.C. proper looking for more FEV, not because there were a lot of people there.
They mention so themselves in dialog, and Reilly suggests at it as well.